The Electrical Potential Difference Across the Cell Membrane of Heart Muscle

The electrical potential difference across the cell membrane of heart muscle cells is a diffusion potential arising from the interaction of fixed charges within the membrane pores with NaCl and KCl diffusing into and out of the cell. The magnitude and sign of this potential difference depend on the relative permeabilities, of the membrane to K, Na, and Cl. The resting membrane is predominantly permeable to K, while the action potential is characterized by a transient increase in Na permeability. An intracellular solution of high K concentration and low Na concentration is separated by the cell membrane from an extracellular solution having a low K concentration and a high Na concentration. These concentration differences are maintained by active transport processes that utilize the energy derived from cellular metabolic reactions to transport Na and K "uphill" against electrical and concentration gradients.