[Effect of niflumic acid on the components of inactivation of the sodium channels of the Ranvier node membrane].

In voltage clamp experiments on the frog Ranvier node, niflumic acid did not alter fast or slow inactivation time courses in the wide range of membrane potentials but reduced the amplitude of the fast phase of inactivation. Fast and slow currents, corresponding respectively to fast and slow phases of inactivation, reversed at the same voltage, revealed different activation- and inactivation-voltage dependences both in intact fibre and after application of niflumic acid. The latter induced a shift of the steady-state inactivation curves for both components of inactivation towards more negative potentials without changing their steepness. The validity of suggestion of the existence of two populations of sodium channels in nerve membrane, is discussed.