1. The role of Ca 2+ in the control of renin release was investigated using a collagenase-dispersed rat kidney cortex cell preparation. 2. Superfusion with a series of low [Ca 2+ ] buffers in either ascending or descending order of concentration increased renin release. Exposure to 0.06 mmol/l Ca 2+ 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 Ca 2+ 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 Ca 2+ 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 [Ca 2+ ], 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 [Ca 2+ ] increases renin release by a mechanism which is independent of changes in adenosine 3′:5′-cyclic monophosphate production. 6. Effects of low [Ca 2+ ], diltiazem and TMB-8 on renin secretion were all shown to be reversible when superfusion with control buffer was resumed.

1. A dynamic column superfusion system has been developed for the study of renin secretion in rat renal cortical cells. 2. Cells were isolated by collagenase digestion and mechanical dispersion, before suspension with polyacrylamide beads and superfusion with oxygenated physiological medium. 3. Renin was detected in the superfusate by incubation of fractions with excess nephrectomized sheep substrate in the presence of angiotensinase inhibitors followed by radioimmunoassay of the angiotensin I generated. 4. Optimized methodology included a purposebuilt polytetrafluorethylene flow cell, a 1 h equilibration to achieve a steady state, 5 min eluate collections, a 15 min stimulatory and a 30 min recovery period, and duration of perfusion of up to 270 min. 5. Significant increments above baseline renin release were seen with the stimuli of adrenaline, noradrenaline and isoprenaline. These could be demonstrated with concentrations of 10 −9 mol/l (adrenaline), 5 × 1O −10 mol/l (noradrenaline) and 1O −9 mol/l (isoprenaline). 6. This technique has significant advantages over previous methods for the study of renin secretion in vitro at the cellular level. It is reproducible and sensitive, and avoids many of the limitations of static cell suspension and kidney slice methods.