Intracellular and extracellular action potentials in frog muscle fibre upon blocking the potassium conductivity.

The dependence between intra- and extracellular action potentials of single muscle fibre of Rana ridibunda when 4-aminopyridine is applied for blocking the potassium conductivity of the membrane was investigated. The changes in the intracellular action potential reflect the degree of the blocker's effect. The initial part of this potential remains practically unchanged. A considerable prolongation of the repolarization phase is observed until a plateau-type potential is established. The extracellular action potentials recorded close to the fibre do not manifest substantial changes. Conclusions are reached about the importance of K-currents for the shape of the extracellular action potential shape.