Sensitivity of the sodium and potassium channels of Myxicola giant axons to changes in external pH.

Abstract

Myxicola giant axons were studied using standard voltage-clamp techniques in solutions whose pH values ranged from 3.9-10.2. Buffer concentrations of 50 mM or greater were necessary to demonstrate the full effect of pH. In acidic solutions the axon underwent a variable depolarization, and both Na and K conductances were reversibly depressed with approximate pKa of 4.8 and 4.4, respectively. The voltage dependence of GNa [number of ions moved/100eV] was only slightly altered by acidic conditions, whereas there occurred large shifts in GK along the voltage axis consistent with a substantial decrease in net negative surface charge in the vicinity of the K+ channels. The Na and K activation rate constants were decreased by acidic conditions, but could not be described as a simple translation along the voltage axis.