On the role of calcium in the electrical responses of cockroach salivary gland cells to dopamine.

1. The calcium dependence of the intracellularly recorded hyperpolarizing responses of salivary gland acinar cells of Nauphoeta cinerea (Olivier) to ionophoretically applied dopamine has been examined. The results of withdrawing calcium from the bathing solution were essentially the same whether or not other divalent cations were present. The effects of calcium withdrawal were rapidly reversed on replacement of calcium. 2. Small responses to dopamine were reduced or abolished by calcium withdrawal but could be restored by an increase in the amount of ejected dopamine. Calcium withdrawal did not have any consistent effect on the input resistance: a reduction in input resistance is therefore not the main cause of the reduction in the amplitude of the responses to dopamine. 3. In very low calcium solutions responses elicited by repeated prolonged dopamine applications progressively declined. 4. It is suggested that the hyperpolarizing responses to dopamine depend on an influx of calcium into the cytosol from a store which can be replenished only from the exterior.