Calcium-dependent regenerative responses in rods

Abstract

NEURONES are thought to contain ion-selective channels whose opening and closing are regulated by the potential difference across the plasma membrane. It is thought that the sodium, potassium, and calcium currents which generate action potentials and modulate synaptic transmitter release pass through these channels. Investigations of voltage-dependent currents in various species have revealed remarkable uniformities in the ion selectivity and pharmacology of presumed membrane channels^1–3. The use of agents which block specific currents has provided a tool for the identification of voltage-dependent conductances in nerve membrane, which we have used to investigate vertebrate photoreceptors. We show here that when the retina of the toad Bufo marinus is superfused with Ringer containing 6–12 mM tetraethyl ammonium (TEA), rods generate oscillations and action potentials resembling the calcium spikes which have been described in various vertebrate and invertebrate preparations³. These experiments demonstrate that the rod membrane is not passive, as is often assumed, but contains at least one and probably two voltage-dependent conductances.