core physiology Flashcards
what is the composition of the cell membrane?
Lipids - 42%
Proteins - 55%
Carbohydrates - 3%
what are the three types of transporter proteins?
Carriers, Pumps and Channels
which transporter requires ATP?
Pump
name the two methods of measuring membrane potential?
patch clamp and glass electrode
how would you go about using the glass electrode technique?
impale cell so the tip (filled with KCl) sits in the IC compartment - measure potential with respect to referee electrode
which technique would have the most specificity
small electrode as much smaller with very sharp tip and insoluble thin wire
what is the distribution of sodium
EC - 150 IC - 15
what is the distribution of potassium
EC - 5 IC - 150
what is the distribution of large organic anions
EC - 0 IC - 65
describe the key features of Na/KATPase
contributes 20% directly
electrogenic - 3 Na out, 2 K in - therefore lose 1 positive charge each time
indirect IC Na and K maintained
if blocked - instantly wipes out membrane potential
what does electrogenic mean
produces a change in electrical potential of cell - change in voltage plus a change in permeability of membrane
what do K+ channels contribute to membrane potential
-ve charge created when K+ moves
creates driving force for K+ to move into cell
equal - opposite movement of K+ means equilibrium
what do Na+ channels contribute
same as K+ - maintain equilibrium
what does the Nernst equation calculate
equilibrium potential of the cell
what is the predictive potential of Na and K
Na - +61.5mV K - -90.8mV
why are the predictive values not = -70mV
because there must be some leakage going on meaning Na can get into the cell and K can leave
what does the Goldman equation calculate
equilibrium potential of cell with more than one ion
what is the relationship between pH and [H+]
increase pH doubles/halves [H+]
how do we measure IC pH
using 2 microelectrodes - change in voltage = change in pH
what are the electrodes calibrated with
pH standards
what are the ideal cells for microelectrodes and why
nerves, muscles, Xenopus oocytes because they are large cells
what could you use to calculate pH of small cells i.e. epithelia
fluorescent indicators
how?
load cells with inactive form (so it can pass through the membrane)
inside cell it is converted to active form
excites a light with specific wavelength - amount at 2nd wavelength is measures
fluorescence = IC pH
indicator is calibrated inside cell and membrane is permeabilised and pH of bath solution is changed
what are the three factors in controlling IC pH
buffers
acid loading
acid extrusion
what do buffers do
moderate effects of acid/alkali load by consuming/releasing protons
DO NOT PREVENT CHANGE pH!!!!
what do buffers rely on
COOH group and NH2 group
what exchanger is used for acid extrusion and hoe does it act
Na/H exchanger protein - exchanges one Na into cell for one H out
what does it rely on
Na gradient set up by Na/K pump
does high pH inhibit or activate exchanger
high pH inhibits - low pH activates
what happens when allosteric modification occurs
a unused proton binds the the allosteric site increasing activity
what is NHE1
housekeeping function with a primary role of regulating pH
what inhibits NHE1
low conc of amiloride plus its analogue EIPA
where is NHE1 found
basolateral membrane of epithelial cells
what exchanger is involved in acid loading and what does it do
Cl/HCO3 exchanger - 1 Cl in and 1 HCO3 out
is it inhibited by high or low pH
inhibited at low pH and activated at high`
what family does this exchanger belong to and how many subtypes are there
the anion exchanger family (AE) - 4 subtypes
what are they all inhibited by
DIDS
do these exchangers rely on Na gradient
no they are independent of Na conc
where is AE1 predominantly found and what shift is it responsible for
RBCs but also in kidneys - hamburger shift/chloride shift
when is there no net proton flux
Je = Jl
why is important to control IC Na+ - epithelial cells
creates gradients that allow uptake of other molecules
excitable cells?
need high chemical gradient to create action potentials
what is Na/K pump inhibited by
glucosides such as ouabain and digoxin
what does Na/K pump do
maintains low IC Na snd high IC K
what are the two roles Na/K pump has in membrane potential
electrogenic
accumulation of K inside cell -MAJOR FACTOR
why is Na/K pump only found in physiologically significant pathways such as collecting duct and excitable cells
requires ALOT of energy
what are normal compositions of Ca
EC - 1mM IC - 100nM
why is Ca regulation important
important secondary messenger in important signalling pathways
what are the two mechanisms in keeping low IC Ca
Na/Ca exchanger
Ca ATPase
describe Na/Ca exchanger
usually exchanges EC Na for IC Ca
stoichiometry means effect of Na influx is magnified as 3Na:1Ca
what family is Na/Ca exchanger
SLC8 family in mammals 3 forms exist
what family is Ca ATPase
P-type ATPase family
describe each type of Ca pump
PMCA - plasma membrane Ca pump - Ca out of cell
SERC - smooth endoplasmic reticulum Ca pump - pumps Ca into organelles for storage
SPCA - Golgi Ca pump - also transports Mn
what are the 4 mechanisms of Ca signalling
VOCC
ROCC
MACC
SOCC
VOCC
voltage operated calcium channel
found in excitable cells
activated by depolarisation
ROCC
receptor operated calcium channel
found in secretory cells + synapses
activated by agonist binding e.g. NMDA
MACC
mechanically activated calcium channel
stretch activated
found in cells that respond to deformation
SOCC
store operated calcium channel
activated following depletion in Ca stores
what are the two store pathways
IP3 receptors activate channel - ubiquitous
ryanodine receptors - low conc activates channel - high inhibits - also activated by caffiene - usually only in excitable cells
