Role of potassium channels in the control of renin secretion from isolatedperfused rat kidneys

This study aimed to assess the relevance of specific potassium channels, su ch as inwardly or outwardly rectifying and calcium-regulated potassium chan nels, to the control of renin secretion. For this purpose we examined the e ffects of the: K+ channel blockers 4-aminopyridine (1 mmol/l), barium (100 mu mol/l), tetraethylammonium (2 mmol/l) and apamin (200 nmol/l) on basal r enin secretion, on renin secretion stimulated by isoproterenol (10 nmol/l) and oil the inhibition of renin secretion by angiotensin II (100-300 pmol/l ) in the isolated rat kidney perfused at constant pressure. Whilst all four K+ channel blockers increased renal vascular resistance, only 4-aminopyrid ine and barium attenuated isoproterenol-stimulated renin secretion in an ad ditive fashion and augmented the inhibitory effect of angiotensin II. These effects of K+ channel blockers were not changed by the L-type calcium chan nel blocker amlodipine (5 mu mol/l), indicating that their effects on renin secretion are not due to voltage-operated calcium influx. Our data, moreov er, suggest that potassium efflux from renal juxtaglomerular cells is not i mportant for the inhibitory action of angiotensin II on renin secretion. As a consequence it appears that the membrane potential of renal juxtaglomeru lar cells per se is relevant to renin secretion such that membrane depolari zation inhibits the exocytosis of renin whilst hyperpolarization favors ren in secretion. By their activity, potassium channels can contribute to membr ane hyperpolarization and thus facilitate renin secretion.