Effects of changing external potassium and chloride concentrations on the photoresponses of Bufo bufo rods.

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Abstract
Intracellular responses to light were recorded from B. bufo rods in different ionic media. The exposure of the retina to high external [K+] depolarized the rod and modified the time course of the photoresponse. The prominent initial transient of rod responses to bright flashes was drastically reduced in 5 mM-external [K+] and completely disappeared in 26 mM. In high external [K+] the kinetics of responses to dim flashes were considerably slower than in control conditions. When external [Cl-] was changed from 120.6-10.6 mM the resting membrane potential decreased and the size of photoresponses increased. Changes in the kinetics similar to those in high external [K+] were observed. In many cases exposure of the retina to low external [Cl-] induced oscillations of the resting membrane potential that sometimes became sustained. This instability of the membrane completely disappeared upon restoring to normal conditions. A voltage- and time-dependent conductance may be active near the dark level of membrane potential. An equivalent electrical circuit with an inductance (Detwiler, Hodgkin and McNaughton) is representative.