7/26/2019 Pset-2015

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Cell Biology Problem Set: Membrane Potentials and Excitability Colin Nichols 10/6

1. Consider the following concentrations (all are given in mM) found in a typical mammalian cell.

Complete the tale y calculating the e!uilirium potential (Nernst "otential) for each ion.

ion #$tracellular %ntracellular #ion(m&)Na' 1

*' 10Ca'+ + 1 , 10-

Cl- 1+0

+. he relative permeailities to *' Na'and Cl-are as follows (with "Ca+' 0)

"*' "Na' "Cl- 1 0.01 +

#stimate &m using the 23* e!uation.

4. %f the relative permeailities suddenly ecame 0.1 + how would &m change5

. he specific capacitance of most cell memranes is 1 7 / cm+.a) 3ow many *'ions must cross the memrane of a spherical cell 0 m in diameter

to change the memrane potential y 10 millivolts.

) 3ow many millimoles does this represent.c) 8hat change in cytoplasmic *'concentration will occur5

. a) 9:etch an action potential (voltage versus time) that appro$imates what is seen in a ventricular

myocyte.) 9uperimpose an action potential that might result if the numer of voltage-gated * channels

were sustantially reduced ut all other conductances were unaffected.

c) 9uperimpose an action potential that might result if the numer of Ca channels weresustantially reduced ut all other conductances were unaffected.

6. %f the p3 outside of a cell is ;. and the p3 inside the cell is ;.+a) 8hat is the Nernst potential for protons across the cell memrane5

) %n what direction will the net flow of protons occur through a surface memrane proton channel

at the following memrane potentials -