When a microelectrode is passed across the cell membrane into the intracellular space of a normal resting myocyte, it records a resting transmembrane potential of approximately -85 mV. At this level, there is no movement of potassium ions thru the potassium channels in the membrane because the electrical driving force, i.e. the difference between the resting membrane potential (-85 mV) and the potassium equilibrium potential (-90mV) is close to zero. There is also no movement of sodium across the membrane even though the electrical driving force for sodium, (-85mV -(+40mV)) is quite large. This is because the conductance for sodium ions (gNa) at this transmembrane potential is very low.