The effect of cadmium on the light-sensitive current in isolated rods of the tiger salamander.

The effect of cadmium on the light-sensitive current of isolated rods of the tiger salamander was analysed by rapidly changing the ionic medium using the technique of Hodgkin et al. (1985). Addition of millimolar amounts of cadmium to the extracellular medium caused a rapid, but transient, decrease of the photocurrent. The effect of cadmium on the movement of divalent cations, such as Ba2+ and Ca2+, differs according to the experimental protocol: when cadmium is introduced into the bathing medium at the same time as Ca2+ or Ba2+, it blocks the entry of these ions into the rod; and when the rod is exposed to cadmium first for a few seconds the entry of Ca2+ and Ba2+ is enhanced. The effect of cadmium is best explained as a dual effect: firstly, an external effect on the channel, and secondly, by metabolic changes, which are caused by a drop of intracellular Ca2+.