What is the force that it would take for a molecule of sodium to spontaneously go through an ion channel in frog muscle? The concentration of Na+ inside and outside of muscle cells is 10.4 mM and 109 mM, respectively; the temperature is 285 Kelvin; and the Vm, or resting membrane potential, is −60 mV. The gas constant and Faraday constant are 8.31 joules/mol·K and 9.65 × 104 coulombs/mol, respectively.