Midterm 2

Question 0

What sets up the sodium gradient that is used to drive the secondary active cotransporters on the apical membrane of the renal tubule?

Answer 0

Na/K ATPase. 3 Na out through the basolateral membrane, 2 K into the epithelial cell. This is a primary active transport.

Question 1

What are diuretics used to treat?

Answer 1

Hypertension, cardiac insufficiency (heart failure), pulmonary edema, and renal failure.

Question 2

Prolines and glycines are found in the TM regions of cotransporters. What are their functions?

Answer 2

They work to kink these regions to form binding substrates right in the middle of the membrane. They are involved in hinging and conformational changes, very flexible.

Question 3

Proximal Convoluted Tubule

Answer 3

60-70% of Na absorbed, 60-70% of water absorbed (follows the sodium). Leaky epithelium, permeable to water. Most diuretics act later in the tubule. Na/glucose,amino acid symport. Na/Cl symporter. Na/Proton antiporter. Na/K ATPase on basolateral membrane. Site of absorption of bicarbonate.

Question 4

Osmotic Diuretics

Answer 4

Mannitol, similar to glucose but can’t be reabsorbed. Osmotic diuretics are filtered in the glomerulus but cannot be reabsorbed in the nephron. They reduce the passive reabsorption of water. Site of action is the proximal tubule and the descending loop of henle. Used in acute renal failure to keep fluid flowing in the nephrons, and for emergency treatment of intracranial or intraocular pressure (not kidney effects). Not useful for controlling blood pressure.

Question 5

Carbonic anhydrase inhibitors

Answer 5

Acetazolamide. Not used as a diuretic because other mechanisms can lead to bicarbonate reabsorption downstream and they can cause a drop in pH that can cause problems. Used in the treatment of glaucoma (involves intraocular pressure). They deplete extracellular bicarbonate and can cause metabolic acidosis.

Question 6

Loop of Henle

Answer 6

Key control of osmotic balance in the body. Ascending limb (thick part) actively reabsorbs Na. Ascending limb is poorly permeable to water, enabling an osmotic gradient. Descending limb is permeable to water but not to salts. The descending limb works passively and is a primary region for water reabsorption due to hypertonic interstitia. Countercurrent exchange mechanism: absorption of salt in the ascending limb is coupled to absorption of water in the descending limb; so the two work together.

Question 7

Vasa recta

Answer 7

Involved in counter current exchange. Blood vessels that branch from efferent arteriole that carry reabsorbed salt and water out of the kidney. Slow blood flow prevents wash out of salts and maintains a high is molarity at the inner medulla.

Question 8

Ascending limb of the loop of Henle

Answer 8

~25% of Na reabsorbed. Na/K/2Cl cotransporter. Low water permeability. Loop diuretics block Na/K/2Cl cotransporter by binding to the Cl site. These are the most powerful diuretics (high efficiency). Used to treat salt and water overload (cardiac insufficiency and pulmonary edema). Antihypertensives, but thiazides are preferred if there’s good renal function.

Question 9

Distal Convoluted Tubule

Answer 9

5-10% of Na reabsorbed, Na/Cl cotransporter. Thiazides diuretics: block Na/Cl cotransporter by binding to Cl site. Less powerful than loop diuretics. Widely used as anti hypertensives and treat cardiac insufficiency. Thiazides have the ceiling effect whereas loop diuretics don’t.

Question 10

Collecting duct

Answer 10

1-5% of Na reabsorbed. Na channel is key to Na reabsorption, electrogenic. K excretion coupled to Na reabsorption. Under hormonal control (aldosterone and vasopressin: SEE PICTURE). K sparing diuretics: Na channel blockers, competitive antagonists of aldosterone. Limited diuretic efficiency. Given with loop or thiazide diuretics to prevent K loss.

Question 11

Collecting duct summary

Answer 11

Na flows down concentration gradient into renal epithelial cells. Na influx through Na channels causes voltage change, resulting in K efflux into tubular fluid and K loss in urine. Aldosterone promotes Na channel activation, synthesis of Na/K ATPase, Na/ proton cotransporter activation. Diuretics (Na channel blockers: amiloride, triamterene, and aldosterone competitive inhibitor spirolactone) are K sparing: Na and water are excreted in urine, K is retained in body. Vasopressin (ADH) causes insertion of aquaporins and reabsorption of water.

Question 12

Bartters syndrome

Answer 12

Too much NaCl excretion, hypotension, neonatal presentation, more severe than gitelmans. (defective Na/K/2Cl cotransporter or K channel or Cl channel in the ascending limb of loop of henle).

Question 13

Gitelmans syndrome

Answer 13

Too much NaCl excretion, hypotension, presentation in early adulthood, (defective Na/Cl cotransporter in the distal tubule).

Question 14

Liddles syndrome

Answer 14

Autosomal dominant, hypertension (mutation in amiloride-sensitive Na channel resulting in more Na channels in plasma membrane than normal). Too much Na reuptake. How can it be treated?

Question 15

Vasopressin

Answer 15

Secreted into the body and transverse the whole body, but it’s main target is the kidney. Vasopressin binds to V2 receptors located in the collecting duct which has downstream effects of inserting aquaporins into the apical membrane. This works to increase water reabsorption, thereby raising blood pressure and decreasing the amount of urine excretion in the process.

Question 16

Diabetes mellitus

Answer 16

Too little insulin produced or cells unresponsive to insulin; excess glucose in blood causes glucose and water loss into the urine (causes renal effects but the cause is not the kidneys). Too much urine, and it is sweet.

Question 17

Diabetes insipidus

Answer 17

Too little vasopressin produced, or collecting duct is unresponsive to vasopressin; results in excess water loss into urine. Urine is not sweet.

Question 18

What are the two main types of diabetes insipidus?

Answer 18

Nephrogenic and neurogenic. Nephrogenic is less common and involves an inability of the kidneys to respond to vasopressin. This can be either an acquired kidney disorder or due to defective V2 receptors (nonfunctional or doesn’t appropriately traffic to the plasma membrane). Neurogenic is the most common and involves a deficiency in vasopressin production. Treated with desmopressin (a vasopressin analogue).

Question 19

What are some diseases that involve protein mistrafficking?

Answer 19

Lysosomal diseases, cystic fibrosis, diabetes insipidus, retinitis pigmentosa, neurodegenerative diseases.

Question 20

What happens to proteins that are misfolded or unassembled?

Answer 20

They are ubiquitinated then degraded by ERAD.

Question 21

How do pharmacological chaperones work?

Answer 21

Give the cells a reagent that causes protein to fold correctly and more quickly and reliably. So you can give an agonist or antagonist into a functional site on the protein, which might help the protein assume it’s correct conformation because it could act as a template.

Question 22

What are the criteria for identifying cotrabsporters?

Answer 22

Physiology: cotransporter ls require the presence if both transported substances to function. Pharmacology: are they blocked by the appropriate drugs? Anatomy: are they found in the right place?

Question 23

Bumetanide

Answer 23

A loop diuretic.

Question 24

What are the sites for blood pressure control?

Answer 24

Heart: decrease in force and rate of cardiac contraction. Kidney: decrease in blood volume. Blood vessels: relax vascular smooth muscle.

Question 25

Treatments for hypertension and control of blood pressure.

Answer 25

ACE inhibitors (decrease angiotensin II). Angiotensin II receptor antagonists. Diuretics (kidney: decrease Na reabsorption, decrease blood volume). Calcium channel inhibitors (blood vessels: causes vasodilation of smooth muscle). Beta-adrenergic receptor antagonists (heart: decrease cardiac output). Alpha1-adrenergic receptor antagonists (blood vessels: block vasoconstriction by alpha1-adrenergic receptors.

Question 26

What process tells the body that it needs more salt?

Answer 26

Juxtaglomerula cells are the sites of secretion of renin. This region of the kidney is in contact with the ascending limb of the distal tubule. Macula densa cells sense the amount of sodium and salts absorbed. Contact between the macula densa cells and the juxtaglomerula cells allows for communication to ensure renin release at appropriate times. The juxtaglomerula cells are prevalent at the afferent arteriole.

Question 27

Afferent arteriole

Answer 27

Low blood pressure can be detected here and stimulates renin release. The area at which renin is release is innervated with sympathetic nerves.

Question 28

How does angiotensin II work?

Answer 28

Renin release leads to several intermediates being synthesized, ultimately leading to increased angiotensin II. Angiotensin II works as a circulating hormone that interacts with the adrenal cortex. The outer region of the adrenal cortex is where aldosterone is synthesized. Angiotensin II activates a GPCR that works to stimulate aldosterone synthesis. Aldosterone is then released into the blood. Aldosterone is a steroid and works through a nuclear receptor. Aldosterone interacts with it's receptor at the collecting duct of the kidney where it causes reabsorption of salt. Increased salt reabsorption leads to decreased urine volume and increased blood pressure.

Question 29

How does renin work?

Answer 29

Renin is a hormone and an enzyme. Renin cleaves angiotensinogen to angiotensin I. Angiotensinogen is made in the liver but is circulating through the blood supply. Angiotensin I is not biologically active, but is converted to angiotensin II by angiotensin converting enzyme (ACE) which cleaves the 2 amino acids on the C terminal side creating angiotensin II, a very active hormone and is an 8 aa peptide. Angiotensin II can then cause aldosterone secretion.

Question 30

How does aldosterone work?

Answer 30

Angiotensin II causes aldosterone secretion. Aldosterone goes to the collecting duct and causes salt reabsorption by increasing the synthesis of sodium channels and sodium channel mediators and sodium potassium ATPases. Angiotensin II is the most powerful vasoconstrictor and has feedback inhibition.

Question 31

How does angiotensin II cause aldosterone synthesis?

Answer 31

Aldosterone is derived from cholesterol. The rate limiting step in aldosterone synthesis is cleavage of a side chain of the cholesterol which is catalyzed by angiotensin II. Angiotensin II also activates a number of enzymes involved in aldosterone synthesis. Angiotensin II acts directly on the blood supply to increase construction of blood vessels. Angiotensin II also increases the release of vasopressin, which also works to cause water reabsorption and increase blood pressure. So the net result is salt and water reabsorption along with an increase in blood pressure.

Question 32

Actions of angiotensin II

Answer 32

- promotes aldosterone synthesis and release, thereby increasing sodium reabsorption in the kidney. - direct vasoconstrictor causing increase in blood pressure. - promoted vasopressin release from posterior pituitary, causing water reabsorption in kidney.

Question 33

Captopril

Answer 33

And ACE inhibitor that binds to the active site of ACE. By knowing the steric restrictions of the active site, Captopril was developed. ACE inhibitors also prevent the breakdown of Bradykinin (a vasodilator) which ACE normally breaks down. Another ACE inhibitor is lisinopril.

Question 34

Angiotensin II receptor antagonists

Answer 34

Block the effects of angiotensin II and are anti hypertensives. It's the AT1 angiotensin II receptor that's responsible for the blood pressure effects of angiotensin II, so inhibitors of AT1 act as anti hypertensives (Sartans e.g. Losartan).

Question 35

Renin inhibitors

Answer 35

Block the active site of renin to prevent proteolysis of angiotensinogen to angiotensin I; are recent drugs to treat hypertension. Aliskiren

Question 36

What are some general principles for G protein signaling?

Answer 36

- cascade of signaling molecules. - signaling is slower than ligand-gated ion channels (but still fast) and persists longer. - amplification of response is intrinsic to this mode if signaling. - multiple downstream targets and multiple responses are frequently produced. - integration and overlap of responses to different hormones/neurotransmitters.

Question 37

What are the two major groups of G proteins?

Answer 37

Small G proteins (ras, rho, rab): monomeric G proteins involved in proliferation, nuclear transport, vesicle transport via effector proteins (e.g. MAP kinase pathway). Heterotrimeric G proteins: coupled to 7 transmembrane spanning receptors. Signaling by hormones and neurotransmitters. Heterotrimeric, consisting of alpha, beta, and gamma subunits. Alpha subunit is related to the small G proteins.

Question 38

Guanine nucleotide Exchange Factors (GEFs)

Answer 38

Activate G protein by promoting GDP release which allows for GTP to bind and activate the receptor.

Question 39

GTPase Activating Proteins (GAPs) also known as Regulators of G-protein Signaling (RGSs)

Answer 39

Inactivate G protein by increasing GTPase activity. GAP= regulate GTPase activity of small G proteins. RGS= regulate GTPase activity of heterotrimeric G proteins.

Question 40

Which steps of GPCRs show amplification?

Answer 40

Receptor -> G proteins adenylyl Cyclase -> cAMP Protein kinases -> phosphorylation of downstream targets.

Question 41

Gs

Answer 41

Stimulates adenylyl cyclase, gives higher concentration of cAMP, higher levels of protein kinase A.

Question 42

Gi

Answer 42

Inhibits adenylyl cyclase, gives lower levels of cAMP, lower levels of protein kinase A activity. Beta/ gamma subunit mediates potassium channel activation.

Question 43

Gt

Answer 43

Increases activity of cGMP PDE, decreasing levels of cGMP, closing cation channels.

Question 44

Gq

Answer 44

Increased activity of Phospholipase C, increase in IP3 and DAG. DAG activates protein kinase C. IP3 increases calcium levels which activated CaM kinase.

Question 45

Can GPCRs open ion channels?

Answer 45

Yes

Question 46

How does GTP binding initiate a conformational change to create an effector binding site?

Answer 46

The gamma phosphate of GTP forms hydrogen bonds with glycine and threonine residues on the switch II and switch I regions respectively. This causes a conformational change rearranging the switch II and I regions and creates a binding site to activate G protein effectors.

Question 47

How is the turn-off of G protein regulated?

Answer 47

Regulation is via control of the rate-limiting step in G preprint turn-off: intrinsic hydrolysis of GTP to GDP by G alpha subunit is very slow, but can be accelerated by GTPase Activator Proteins (GAPs; RGS proteins). RGS proteins order the catalytic residues in G alpha to optimize GTP hydrolysis. Inactivation of G protein is favorable because it is coupled to hydrolysis of the high-energy phosphodiester bond of GTP.

Question 48

Guanine Nucleotide Dissociation Inhibitors (GDIs)

Answer 48

Prevent GDP dissociation. Lock the small G protein in the GDP-bound inactive state, and shield their prenyl groups, this preventing their localization to the membrane. GDIs for heterotrimeric G proteins: GoLoco proteins bind to the G alpha in the inactive GDP state. This results in decreased G alpha signaling, but increases G beta gamma signaling because the GDIs competitively block reassociation of G beta gamma with G alpha.

Question 49

GPCR class A

Answer 49

GPCRs that bind small molecules in which the ligand binds to the TM region.

Question 50

GPCR class B

Answer 50

GPCR that binds larger molecules in the extracellular domain.

Question 51

GPCR class C

Answer 51

GPCR that binds calcium, glutamate, GABA, pheromones; at an extracellular domaine resembling a clam shell.

Question 52

Why do some GPCRs dimerize?

Answer 52

One of the receptors may have a trafficking motif that allows for the dimer to get to the plasma membrane. May need to bind 2 Ligands for activation. May affect the type of G protein activated.

Question 53

How is a GPCR signal terminated?

Answer 53

GRK phosphorylated an activated receptor, which promotes the binding of arrestin which blocks the G protein binding site.

Question 54

GPCR desensitization

Answer 54

Involves uncoupling from G protein and receptor internalization. Can be homologous, in which the receptor itself binds agonist, after it's activated GRK phosphorylates it, arrestin binds it, and it stops binding G protein. Heterologous desensitization involves a different receptor becoming active which signals downstream pathways that can go back and phosphorylate the GPCR in other ways (not the same sites as GRK is phosphorylating) and continue to down regulate and uncouple the GPCR from the G proteins.

Question 55

What are 2 activities of thrombin?

Answer 55

Cleaves fibrinogen to fibrin which can then form a network emmeshing platelets and red blood cells in a clot. Can activate a protease activated receptor which stimulates lymphocyte cell division, platelet aggregation, and is a chemotactic for monocytes.

Question 56

How do proteinase activated receptors work?

Answer 56

Protease proteolytically cleaves the receptor to activate it. The receptor has an elongated amino terminus that has a cleavage site that the protease can attack. Thrombin cleaves the amino terminus, which generates a new amino terminus that has a recognition site that acts as a tethered agonist that binds to the GPCR itself and activates the receptor. An internally activated receptor.

Question 57

How can you turn off a permanently activated PAR?

Answer 57

Internalize the receptor, or inactivate the receptor by downstream cleavage.

Question 58

What's an example of a GPCR that's turned on too much?

Answer 58

Hyperthyroidism. Somatic mutation in the 3rd intracellular loop of thyroid stimulating hormone receptor which makes it always on. Thyroid is produced too much and can result in goiter from growth and differentiation of thyroid adenoma. Also retinitus pigmentosa involves a GPCR that is on too much.

Question 59

What are some general principles of second messengers?

Answer 59

Small molecules. Diffusible (either membrane bound or soluble). Rapidly synthesized. Rapidly degraded. Spread of signal. Amplification of response. Provide rapid, amplified transduction of signal.

Question 60

How can cAMP levels be regulated.

Answer 60

Regulate adenylyl cyclase or regulate cAMP phosphodiesterase.

Question 61

Phosphodiesterase inhibitors

Answer 61

Methyl xanthines (look kind of like a nucleotide): caffeine and theophylline (used to treat asthma). Theobromine is a weak methyl xanthine. Block the breakdown of cAMP.

Question 62

Cholera toxin

Answer 62

Activates Gs which stimulates adenylyl cyclase. ADP ribosylates Gs.

Question 63

Pertussis toxin

Answer 63

Inhibits Gi which increases activity of adenylyl cyclase. ADP ribosylates Gi.

Question 64

Forskolin

Answer 64

Activates adenylyl cyclase. Bypasses the G proteins.

Question 65

Protein kinase A

Answer 65

PKA has 4 subunits. 2 are regulatory and 2 are catalytic. cAMP binds to sites in the regulatory subunits which initiates a conformational change on the regulatory subunits that releases the catalytic subunits. The free catalytic subunits are then active and can phosphorylate downstream targets resulting in either the activation or inactivation of the targets. PKA phosphorylates Ser and Thr within a consensus site. Regulatory domains of kinases contain inhibitory pseudosubstrate regions that mimic the consensus site but can't be phosphorylated. They work to clog the active site and inhibit phosphorylation. Protein kinase A phosphorylates Ser or Thr within a consensus site.

Question 66

Beta 1 receptors

Answer 66

Increase rate and force of cardiac contraction. Activates Gs. Agonists: ISO>EPI>NE>PE Antagonists: Propranolol

Question 67

Alpha 1

Answer 67

Found in blood vessels of the peripheral vasculature. They increase blood pressure. Activates Gq. Causes vascular smooth muscle contraction. Agonists: EPI> or = to NE>>PE>>ISO Antagonists: Prazosin

Question 68

Beta 3

Answer 68

Found primarily in fat cells. Increase lipid breakdown. Activates Gs

Question 69

Beta 2

Answer 69

Important in the lungs. Coronary dilation and bronchial dilation. Also found in the liver and initiate break down of glycogen to glucose. Activates Gs. Promotes smooth muscle relaxation. Agonists: salbutamol and salmeterol.

Question 70

Norepinephrine

Answer 70

Increased heart rate and force of contraction, increased blood pressure. Peripheral vasoconstriction.

Question 71

Epinephrine

Answer 71

Increased heart rate and force of contraction, increased blood pressure, peripheral vasoconstriction, increased lipid breakdown, coronary dilation and bronchial dilation, increased breakdown of glycogen to glucose.

Question 72

Alpha adrenergic receptors

Answer 72

Agonists: NE, Epi, >> Isoproterenol

Question 73

Beta adrenergic receptors

Answer 73

Agonists: Isoproterenol >> NE, Epi

Question 74

Sympathetic fight or flight response involves

Answer 74

Glycogenolysis (breakdown of glycogen to glucose), bronchiodilation (opening of lung airways: relaxation of smooth muscle), stimulation of the heart (increased force and rate of contraction: contraction of cardiac muscle), and vasoconstriction (increased blood pressure: contraction of smooth muscle).

Question 75

Alpha 2

Answer 75

Activates Gi. Causes contraction in some vascular smooth muscle. Usually involved in presynaptic inhibition. Agonists: EPI > or = to NE>>PE>>ISO. Antagonists: Yohimbine

Question 76

Vagus nerve

Answer 76

Parasympathetic innervation of the lungs that acts via M3 muscarninic receptors. Regulates vascular smooth muscle tone (extent of contraction). Stimulating causes bronchiole constriction via the Gq pathway.

Question 77

How does sympathetic system work on the lungs?

Answer 77

There's very little sympathetic innervation of the lungs. Epinephrine is carried through the blood and acts as a hormone to stimulate the beta 2 receptors on the lungs.

Question 78

What is asthma?

Answer 78

Recurring reversible airway obstruction. Can be fatal. Underlying features are constriction of the bronchiole tubes and inflammation. Early phase involved bronchospasm and late phase involves inflammation.

Question 79

How is the immediate phase of asthma treated? (Bronchospasm)

Answer 79

Beta 2 agonists, CysLT-receptor antagonists, and theophylline. Also muscarninic M3 receptor antagonists.

Question 80

How is the late phase of asthma treated? (Bronchospasm, wheezing, coughing)

Answer 80

Inhibited by glucocorticoids, which work via nuclear receptors to inhibit inflammation. Can have negative effects on the rest of the body including: inhibition of wound healing, bone repair, and can cause bone loss.

Question 81

Striated (skeletal) muscle

Answer 81

Contracts in response to membrane action potential that changes the activity of the dihydropuridine receptor. The DHPR is very similar to a calcium channel, but in this case it doesn't function as one. Instead it functions as a mechanical stimulus that stimulates an intracellular ryanodine receptor on the sarcoplasmic reticulum. This releases calcium from intracellular stores and causes muscle contraction. Striated muscle involves voltage induced calcium release. Calcium interacts with troponin.

Question 82

Cardiac muscle

Answer 82

Calcium channels on plasma membrane that open in response to a membrane action potential depolarization. Cardiac muscle also has ryanodine receptor on SR. The ryanodine receptor in the heart is responsive to calcium concentrations. Calcium comes in through the plasma membrane, activates the ryanodine receptors, which leads to intracellular calcium release. Together these two sources of calcium cause muscle contraction via interaction with troponin.

Question 83

Smooth muscle

Answer 83

Calcium comes in through the plasma membrane, as well as other sources of calcium. There are also agonists that activate GPCRs (Gq) that increases the production of IP3, which activates calcium release from intracellular stores. IP3 receptors are activated and cause calcium release from the SR. Together the calcium binds calmldulin which binds to MLCK which can then phosphorylate myosin causing contraction.

Question 84

Loop diuretics

Answer 84

Furosemide, bumetanide

Question 85

Collecting duct diuretics

Answer 85

Spirolactone, amiloride, triampterine. Potassium diuretics.

Question 86

Whats are treatments for hypertension, angina, and arrhythmias?

Answer 86

Beta blockers and calcium channel antagonists.

Question 87

Adenosine receptor

Answer 87

Activates Gi in the lungs, leading to decreased cAMP levels via inhibition of adenylyl cyclase. Adenosine antagonist can be a bronchodilator and can inhibit PDE and AC.

Question 88

What is a hirudin site?

Answer 88

Site next to the end of the amino terminus of PARs. Recruits the protease and helps it bind to the active site of the protease. Leeches mimic this site to prevent clotting by competing for the binding of thrombin.

Question 89

A-Kinase Anchoring Proteins

Answer 89

Recruit GPCRs, PKA, downstream effectors, and PDE. A scaffolding protein.

Question 90

Endoglycosylase H and F

Answer 90

H cleaves high mannose, F cleaves both mature and immature glycosylation.

Question 91

How to tell if cotransporters are found in the right place?

Answer 91

Northern blot and in situ hybridization.

Question 92

Alternating access model of transport

Answer 92

Bind to one side and release on the other. Alternate exposure of substrate binding site to each side of membrane.