The effect of holding potential on the asymmetry currents in squid giant axons

Kinetics of calcium inward current activation

“…THE JOURNAL OF GENERAL PHYSIOLOGY 9 VOLUME 73 the m 3 scheme which is formally good for Na channels activation kinetics is not supported by the voltage dependence of gating-charge distribution (Meves, 1974). One cannot exclude that it may be partially due to the especially slow inactivation of Ca current which does not interfere in practice with the activation process.…”

The effect of zinc on the late displacement current in squid giant axons.

“…The apparatus and experimental procedure are fully described in the preceding publication (Meves, 1974). The membrane currents were recorded with a double C electrode which was calibrated by sending a 10 flA current from a 12 mm platinized Pt wire, diameter 1 mm, centred in the double C; the membrane area used for calculating the current density was determined from measurements of the fibre diameter made before extrusion.…”

“…The asymmetrical charge movement is possibly related to the opening and closing of the Na gates. Zn binds strongly to the imidazole group (see Begenisich & Lynch (1974) and Friedberg (1974) for references) to which Clark & Strickholm (1971) have ascribed an important role in the gating of ionic channels; alternatively, the action of Zn on the presumed gating current (which is similar to that of glutaraldehyde, see Meves (1974)) may be related to its cross-linking effect.…”

“…At a holding potential less negative than -60 or -65 mV the signal reverses its sign (i.e. the on-response becomes inward and the off-response outward), suggesting that now Ihyperpol is larger (Keynes, Rojas & Rudy, 1974;Meves, 1974). The experiments described here confirm the observation that internal Zn blocks the normal asymmetry current seen at holding potentials more negative than -60 or -65 mV; they show, however, that the reversed signal (recorded at holding potentials less negative than -60 or -65 mV) is not affected by Zn.…”

“…3, but almost straight lines were obtained in double logarithmic plots log I vs. log t (see fig. 8 of Meves, 1974 (1973) for an imperfect condenser. The time course was not affected by altering the height of the perfusion fluid in the cannula; compensation of the resistance in series with the axon membrane (= 28 L cm2 at 20 C, measured by the method of Moore & Cole, 1963), also had no effect on the slow component of the capacity transient.…”