1. The role of Ca2+ in the control of renin release was investigated using a collagenase-dispersed rat kidney cortex cell preparation.

2. Superfusion with a series of low [Ca2+] buffers in either ascending or descending order of concentration increased renin release. Exposure to 0.06 mmol/l Ca2+ increased release by 120% (P < 0.001) when presented as the first buffer in ascending order of concentration and by 79% (P < 0.001) when presented as the fourth and last in a series of descending order.

3. The Ca2+ entry blocking drug diltiazem in a range of concentrations increased renin release and at 10−5 mol/l diltiazem the mean stimulation was 35% (P < 0.01).

4. 8-(N,N-Diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) reduces the release of Ca2+ from intracellular stores and, studied over a range of concentrations, this compound increased renin release. At 10−5 mol/l TMB-8 the mean increase was 44% (P < 0.001).

5. None of these experimental manipulations, low [Ca2+], diltiazem or TMB-8, had any effect on the release of adenosine 3′:5′-cyclic monophosphate into the cell superfusate, indicating that a decrease in intracellular [Ca2+] increases renin release by a mechanism which is independent of changes in adenosine 3′:5′-cyclic monophosphate production.

6. Effects of low [Ca2+], diltiazem and TMB-8 on renin secretion were all shown to be reversible when superfusion with control buffer was resumed.

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