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Cell physiology and pharmacology > Lecture 13- Intracellular signalling and calcium homeostasis > Flashcards

Lecture 13- Intracellular signalling and calcium homeostasis Flashcards

1
Q

how much calcium in the body

A

1kg

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2
Q

where is most calcium found

A

in bones (99%)

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3
Q

concentration of calcium in the blood serum

A

8-10 mg/dL (50% free calcium)

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4
Q

whole body calcium homeostasis is regulated via

A

• Intestinal calcium uptake • Ca2+ reuptake by the kidney • Bone calcium regulation

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5
Q

how is calcium homeostasis controlled hormonally

A

• Ca2+ sensing receptors in the parathyroid (GPCR) • Parathyroid hormone receptor • Calcitonin receptors • Vitamin D3- nuclear receptors

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6
Q

concentration of calcium in the cytoplasm

A

low 1 x 10^-7 M

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7
Q

concentration of calcium outside the cell

A

high (same conc as blood) 1-2 x10^-3M

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8
Q

concentration of calcium outside in the endoplasmic reticulum/ SR

A

high 2-3 x 10^-4

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9
Q

why is calcium important

A

• Muscle contraction • NT/ stimulus-secretion coupling • Fertilisation • Cell death (apoptosis) • Regulation of metabolism • Learning and memory

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10
Q

plasma membrane is

A

impermeable to calcium

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11
Q

specific pumps and transporters

A

move calcium in and out of the cell

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12
Q

what decrease the free level of calcium

A

buffer proteins within the cytoplasm

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13
Q

channels which decrease intracellular [calcium]

A
  1. PMCA 2. SERCA 3. NXC
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14
Q

PMCA

A

plasma membrane calcium ATPase uses ATP to pump calcium out of the cell

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15
Q

SERCA

A

sarcoplasmic reticulum calcium ATPase Uses ATP to pump calcium in the SR from the cytoplasm

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16
Q

NCX

A

sodium calcium exchanged calcium exchanged for sodium

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17
Q

channels which increase levels of calcium in the cell (Influx)

A

• Ligand gated ion channel • Voltage gated channels

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18
Q

how is calcium moved out of the SR

A
  • Calcium induced calcium release (CICR)- ryanodine receptors - IP3R receptors (think Gq)
19
Q

effectors stimulated by GPCR G protein can be

A

enzymes (2nd messengers) or ionic channels

20
Q

example of ionic channels

A

• Voltage gated calcium channels (VOCCs) • G-proteins evaluated inwardly rectifying K+ channels (GIRKs)

21
Q

example of 2nd messengers

A

• Adenylyl cyclise (ATP —> cyclicAMP) • Phospholipase C (PIP2–> IP3 + DAG) • Phosphoinositide 3-kinase (P13K) • cGMP phosphodiesterase (cyclic GMP —> 5’-GMP)

22
Q

outline agonist binding to Gs GPCR

A
  1. Agonist binds to GPCR
  2. Causes GDP for GTP exchange in G-protein
  3. AlphaS and BY subunits dissociate
  4. AlphaS-GTP activates AC
  5. AC converts ATP to cAMP
  6. cAMP activates PKA
23
Q

cAMP exerts the majority of its effects via

A

PKA

24
Q

PKA structure

A
  • x2 C subunit contain protein kinase subunit
  • x2 R subunit is where CAMP binds
25
Q

how many cAMP bind to each regulatory region

A

2 (4 in total)

26
Q

when cAMP binds to PKA

A

this causes it to release the catalytic subunit (covalent change) , so it can act as a PK and phosphorylate other proteins to activate them (usually phosphorylation serine or threonine residues) - Therefore when CAMP increases so does the activity of PKA

27
Q

outline agonist binding to Gi GPCR

A
  1. Agonist binds to GPCR 2. Causes GDP for GTP exchange in G-protein 3. AlphaI and BY subunits dissociate 4. AlphaI inhibits adenyl cyclase 5. No production of cAMP 6. No activation of second messengers- no signal transduction
28
Q

which G protein is activated to regulate phospholipase C (PLC)

A

Gq

29
Q

outline agonist binding to Gq GPCR

A
  1. Agonist binds to GPCR 2. GDP for GTP exchange in G protein 3. Alphaq – GTP activates phosoholipase C (PLC) 4. PLC catalyses the hydrolysis of PIP2 5. PIP2  DAG (still associated with membrane)+ IP3 6. IP3 diffuses through cytoplasm and binds to IP3 receptros and causes them to open 7. Allows movement of calcium out of SR/ER 8. DAG has its own PK and phosphoryklates PKC
30
Q

IP3 binds to

A

IP3R

31
Q

IP3R activation can

A

increase cytoplasmic [CA2+] by 5-10fold within a few seconds of agonist addition

32
Q

key feature of signalling pathways

A

signal amplification

33
Q

signal amplification

A
  • allows small amount of ligand e.g. hormone to cause a relatively large response within the cells

• E.g. For a few molecules of adrenaline binding to surface of B-adrenoreceptors may cause a massive cellular response

34
Q

inotropy

A

strength of contraction

35
Q

chronotrophy

A

heart rate

36
Q

outline how B1- adrenoreceptors can be stimulated to cause positive inotropy

A
  1. Adrenaline binds
  2. Activates alphas (can also directly activate VOCC) activates AC
  3. AC produces cAMP
  4. cAMP activates PKA
  5. PKA phosphorylates VOCC (voltage gated calcium channels)
  6. Increases intracellular calcium
  7. Increase contractility of the heart
37
Q

sympathetically released noradrenaline interacts with alpha1 adrenoreceptors of smooth muscle

A

vasoconstriction

38
Q

parasympathetic ally release ACh can interact with bronchiolar smooth muscle M3 receptors causing

A

bronchoconstriction

39
Q

smooth muscles all utilise

A

Gq- Phospholipase C (PLC)

40
Q

smooth muscle utilisation of Gq

A

Phospholipase C (PLC) • IP3 causes release of calcium from SR (triggers contraction) • PKC activated (sustained contraction) • Leads to prolonged contraction of the smooth muscle

41
Q

At the presynaptic neurone, GPCRs

A

can regulate NT release

42
Q

BY subunit of G inhibits specific types of

A

Can VOCCs reducing calcium influx and NT release at the synaptic cleft

43
Q

U-opiod reeptor

A
  1. Morphine binds to U-opioid receptor
  2. Gi protein
  3. Activates GI (GDP for GTP exchange)
  4. Causes release of both alpha and BY subunits
  5. BY binds to VOCC and inhibit VOCC
  6. This means that the next time there is a depolarisation, the VOCC is inhibited
  7. Meaning less NT is released into synaptic cleft
  8. Reduced transmission of AP from neurone to neurone

• 80-90% of inhibition

Cell physiology and pharmacology (20 decks)

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