Flurazepam: effects on sodium and potassium currents in myelinated nerve fibres

The effect of flurazepam-HCl on single myelinated nerve fibres of the frog Rana esculenta was investigated. Flurazepam affected both Na and K currents: 0.25 mM of the drug decreased the peak Na inward current to about 50%. The initial increase and subsequent decay of the Na current was slowed down by a factor of 1.5 independent of membrane potential. The drug induced a slow phase in the recovery from Na inactivation and frequency dependence of the Na current block. The K current rose at a normal rate and was then inactivated to a sustained outward current. The time constant of block development (tau k) and the steady state block were potential-dependent. With 1 mM flurazepam, tau k decreased from 2.9 ms at E = 10 mV to 1.5 ms at E = 90 mV, and the steady state block increased from 65% at E = -20 mV to 81% at E = 90 mV. Recovery from the block proceeded faster at E = -70 mV (tau = 27 ms) than at E = -120 mV (tau = 89 ms). The effects of the drug on the K current were interpreted in terms of the reaction scheme proposed by Armstrong (J. Gen. Physiol. 54, 553; 1969).