In order to reveal the characteristics of ion channels, the
in situ rods of the frog retina were stimulated by intracellular current injection. Transient depolar-izations were observed not only at the onset of the application of the depolarizing current, but also at the termination of the hyperpolarizing current. Experiments in perfusate containing ion channel blockers, Co
2+ and TEA, revealed that the both depolarizations were attributed to the activation of the voltage-dependent Ca
2+ current, and appeared transient being counteracted by hyperpolarization due to the voltage-dependent or the Ca
2+-dependent K
+ current. In addition, Cs' ap-plication eliminated a negative transient response produced at the onset of the hyperpolarizing current, suggesting that it was attributed to the h current. All the ion channels observed in
in situ frog rods were identical to those found in enzymatically isolated sa!amander rods, indicating that the cell dissociation procedures did not affect the rod membrane properties. In addition, taking into account the direction of the stimulus current and the rectification of the rod cell membrane, the active site for producing the Ca
2+ response was not restricted solely to the rod terminal, but the inner segment also could produce Ca
2+ response.
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