Rapidly activating hydrogen ion currents in perfused neurones of the snail, Lymnaea stagnalis.

Abstract

SUMMARY1. Cells from the circumoesophageal nerve ring of the pond snail Lymnaea 8tagnali8 were internally perfused with solutions containing Cs aspartate, EGTA and pH buffers. Time-dependent, voltage-dependent 'residual' outward currents were observed at positive potentials. They were found to be carried largely by H+.2. The outward H+ currents were reduced by high internal pH, low external pH, external Cd2+ and 4-aminopyridine. External tetraethylammonium ions reduced the H+ currents but had a more effective blocking action on the K+ currents in these cells. All five agents reduced the maximum H+ conductance. In addition Cd2+, low external pH and high internal pH were found to shift the voltage dependence of the H+ current to more positive potentials.3. There was no significant difference between H+ currents recorded with the internal pCa2+ about 7 and those recorded with the internal pCa2+ near 5.4. It is likely that the H+ channel described here provides the basis for the increase in H+ permeability described by Thomas & Meech (1982) in depolarized Helix neurones.

Changes in intracellular pH associated with glutamate excitotoxicity

“…Yet very little inward current has been observed through H+ channels (Barish and Baud, 1984;Byerly et al, 1984;Decoursey, 199 1). Hf influx through other channel types may also be insufficient for the following reasons.…”

“…One often suggested possibility involves hydrogen ions entering neurons directly either through GLU channels, hydrogen ion channels, or other voltage-activated channels (Thomas and Meech, 1982;Mozhayeva and Naumov, 1983;Barish and Baud, 1984;Byerly et al, 1984;Chesler and Chan, 1988). Yet very little inward current has been observed through H+ channels (Barish and Baud, 1984;Byerly et al, 1984;Decoursey, 199 1).…”

Characterization of a voltage-gated K+ channel that accelerates the rod response to dim light

“…The strong shift is not explained by simple shielding of surface charges, since Ca 2+ at the same concentration failed to produce the same effect as Ba 2+ . There are precedents for specific divalent cations shifting the activation range of voltage-dependent ion channels by amounts exceeding those predicted by simple shielding of surface charges (e.g., Byerly et al, 1984), but such an effect of Ba 2+ on K + channels is novel (for review see Yellen, 1987), and the mechanism for these interactions is unknown.…”

Activation kinetics of calcium currents in bull‐frog sympathetic neurones.

“…A modified form of the constant-field equation as used by Brown et al (1983) can describe the data but it is necessary to incorporate a correction factor for positive potentials. Other authors have reported the observed currents at positive potentials to be carried not only by Ca2+ but also by Cs+ passing through Ca2+ channels (Fenwick et al 1982) or by H+ through distinct channels (Byerly, Meech & Moody, 1984b). The term D in eqn (7) would account for all these contaminating outward currents.…”