Abstract
The purpose of these experiments was to characterize the effects of diltiazem on renin secretion from rat renal cortical slices. Incubation of slices in 60 versus 4 mM K medium almost completely abolished renin secretion. Diltiazem antagonized the inhibitory effect in a concentration-dependent manner but had no effect on secretion of slices incubated in 4 mM K medium. Lowering extracellular Ca enhanced the efficacy of diltiazem. These observations demonstrate that Ca influx through voltage-sensitive Ca channels mediates the inhibitory effect of depolarization and further demonstrate that such channels are not open in the basal state of this preparation. In the presence of a concentration of diltiazem which blocked the inhibitory effects of depolarization, both angiotensin II and antidiuretic hormone (ADH) still inhibited secretion. Therefore, both these peptides inhibit secretion by mechanisms which are independent of the voltage-sensitive Ca channels. These observations confirm and extend previous observations suggesting that Ca plays an inhibitory coupling role in the control of renin secretion.
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