Nat electrochemical gradient Sodium Sodium Sodium chemica, electrical electrochemical radient gradient · gradient (natl …::,/ .- Na EXTRACELLULAR FLUID Geomembran CYTOSOL
17 Na+ electrochemical gradient
Equilibrium potentials >Theoretical voltage produced across the membrane 90 >if only one kind of ion Voltmeter could diffuse through the Intracellular eXtracellular membrane electrode >If membrane onl Fixed anions permeable to K+K+ Electrical attraction diffuses until [k] is at K+K+ K+ K+K+ Diffusion K+ equilibrium >Force of electrical attraction and diffusion are= opposite
18 Equilibrium Potentials ➢Theoretical voltage produced across the membrane ➢if only one kind of ion could diffuse through the membrane. ➢If membrane only permeable to K+ , K+ diffuses until [K+ ] is at equilibrium. ➢Force of electrical attraction and diffusion are = opposite
Calculating equilibrium potential Nernst Equation Allows theoretical membrane potential to be calculated for particular ion Membrane potential that would exactly balance the diffusion gradient and prevent the net movement of a particular ion >Value depends on the ratio of lion] on the 2 sides of the membrane
19 Calculating equilibrium potential Nernst Equation ➢Allows theoretical membrane potential to be calculated for particular ion. ➢Membrane potential that would exactly balance the diffusion gradient and prevent the net movement of a particular ion. ➢Value depends on the ratio of [ion] on the 2 sides of the membrane
Nernst equation RT C Equilibrium potential(mV) Eion zF [C] where [C] and [C] extra and intracellular [ion R= Universal gas constant(8. 3 joules. k-I.mol-) T Absolute temperature( k) F= Faraday constant (96, 500 coulombs. mol-) z= Charge of ion(Na+= +1 Ca2+ =+2 CI-=-1 ForK,withⅨk]。=4mmol.l-andk1]=150 mmol.I-1 At 37 C, Ek =-97mv ENa=+60mv
20 Nernst equation Equilibrium potential (mV) , Eion = ln RT zF [C]o [C]i where, [C]o and [C]i = extra and intracellular [ion] R = Universal gas constant (8.3 joules.K-1.mol-1 ) T = Absolute temperature (°K) F = Faraday constant (96,500 coulombs.mol-1 ) z = Charge of ion (Na+ = +1, Ca2+ = +2, Cl- = -1) For K+, with [K+ ]o = 4 mmol.l-1 and [K+ ]i = 150 mmol.l-1 At 37°C, EK = -97mV ENa = +60mv
● Experimental points Membrane potential (millivolts) -70 (Red line shows values according to Nernst equation) 130 510 100 EXtracellular potassium concentration(millimoles [K*l=4 mmol
21 1 10 100 Extracellular potassium concentration (millimoles) Membrane potential (millivolts) -130 -60 +10 (Red line shows values according to Nernst equation) Experimental points -70 5 [K + ] o = 4 mmol.l - 1