Human skeletal muscle has a voltage-gated proton current

Abstract

A voltage-gated proton current, I H, was studied with the whole-cell patch-clamp technique in human myotubes obtained from biopsies of human muscle. Studies of the reversal potential of I H during substitution of K +, Na +, Ca 2+, Cl −, Cs +, and H + in the extracellular solution indicated that protons were the major charge carriers of I H. This current is similar in many respects, but not identical, to the proton currents already described in other cell types. I H is activated by depolarization and it can be affected by extracellular pH. I H can be blocked by external divalent cations including Ca 2+. This block is voltage-dependent, being more efficient at hyperpolarized than at depolarized voltages. The voltage-dependent properties of I H and its ability to be affected by pH and extracellular Ca 2+ suggest that I H might be used by muscle cells to extrude protons during action potentials.