Modification of K channel inactivation by papain and N-bromoacetamide.

The whole-cell variation of the patch clamp technique was used to study macroscopic K current in voltage clamped GH3 cells. An inactivating, voltage-dependent K current was studied in isolation by inhibiting Ca-activated K currents with internal Ca chelators and external tetraethylammonium ions. Under control conditions, the K current inactivated in two phases with time constants of 25 and 79 ms. After treatment with either a proteolytic enzyme such as papain or the amino acid reagent N-bromoacetamide, the K current no longer inactivated rapidly, but decayed very slowly with a time constant of 500 to 750 ms. The action of papain or N-bromoacetamide on K channels is comparable to their action on Na channels, suggesting that inactivation in Na and K channels occurs by a similar mechanism.