Time‐ and voltage‐dependent ionic components of the rod response.

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Abstract
Electrical properties of individual rods, physically isolated from the vertebrate rod network, were measured by time of response and voltage-current relations. Properties were measured in normal and altered bathing media designed to reveal the ionic basis for the time and voltage dependent properties of the rod response. In normal media the rod membrane was strongly outward-rectifying with slope resistance near 100 M.OMEGA. when hyperpolarized, but near 10 M.OMEGA. when depolarized from a typical ambient level near 35 mV. The membrane become inward rectifying for hyperpolarizations beyond -95 mV, with slope resistance near 70 M.OMEGA.. Normal hyperpolarizing overshoot associated with the rod response was strongly potential dependent; the overshoot in response to a current step disappeared when the membrane was first depolarized or hyperpolarized by more than about 10 mV from the -35 mV ambient potential level. The decay from overshoot, elicited either by current or light, could be approximated with a 1st order time constant of about 150 ms. In the absence of Na the peak-plateau sequence remained intact. Membrane resistance increased during transition to the plateau. The plateau became more hyperpolarized than the early phase during responses beyond -75 mV. These results indicate a time- and voltage-dependent conductance other than Na contributes to the peak-plateau response, probably K. Outward rectification was greatly reduced in the presence of 15 mM-TEA, suggesting that it is mediated by K activation. Inward rectification, and the associated transients near -95 mV were eliminated in the presence of 2 mM-Cesium, suggesting that K conductance contributes to the time and voltage dependent inward rectification.