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BioSubi BioSubi
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9 years ago
A cell has the following distribution of ions across its membrane with the concentrations (activity) given in mmol -1 (mM):

Ion   Inside    Outside

An-    140.5
Na+    9.0       141.0
K+     136.0     4.0
cl-       3.5       119.0
HCo3  1.0         26.0
-
Assume the membrane is permeable to Na+,K+,andCl-, but impermeable to An- (assume univalent) and bicarbonate (HC03-}[Actually cells have mechanisms for transportingbicarbonateacross the membrane,usuallyinexchangefor Cl-,butthese are mainly electroneutral and can be ignored

What cellular mechanism (s) is (are) needed if the cell is to remain in a stable steady state with the concentrations shown in the table? Indicate clearly all factors you have considered.

(i) What is the steady state or resting membrane potential?
(ii) Why can electroneutral ion transporters be ignored in calculations of resting membrane potential? Is this also true for electrogenic transporters?
(iii) What are the short- and long-term consequences of the loss of the mechanism(s) identified in part (i).
(iv) Suppose the membrane was indeed permeable to HCO3- ions, due to the fact that these ions pass quite readily through the Cl- channels present in the cell. Explain qualitatively how this will affect the steady state.
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