Two Types of Voltage-activated Calcium Currents in Goldfish Horizontal Cells

Two Types of Voltage-activated Calcium Currents in Goldfish Horizontal Cells

In horizontal cells (HCs) that were freshly dissociated from goldfish retina, two types of voltage- dependent calcium currents (I<SUB>Ca</SUB>) were recorded using a patch-clamping configuration: a transient type current and a sustained type current. The cell was held at &#8291;40 mV, and the prepulse step of &#8291;90 mV was applied before command pulse between &#8291;65 and &#8290;55 mV. The transient Ca<SUP>2&#8290;</SUP> current was activated by depolarization to around &#8291;50 mV from a prepulse voltage of &#8291;90 mV lasting at least 400 ms and reached a maximal value near &#8291;25 mV. On the other hand, the sustained Ca<SUP>2&#8290;</SUP> current was induced by pre-inactivation for less than 10 ms duration. Its activation started near &#8291;10 mV and peaked at &#8290;20 mV. Co<SUP>2&#8290;</SUP> (2 mM) suppressed both of these two components, but nifedipine (20μM), L-type Ca<SUP>2&#8290;</SUP> channel antagonist, blocked only the sustained current. Based on the activation voltage and the pharmacological specificity, the sustained current appears to be similar to L-type I<SUB>Ca</SUB> and the transient type to T-type I<SUB>Ca</SUB>. This study is the first to confirm that transient type I<SUB>Ca</SUB> together with the sustained one is present in HCs dissociated from goldfish retina.