Electrophysiology of the renin-producing juxtaglomerular cells.

Renin is an aspartyl-proteinase hormone that is produced, stored and released by juxtaglomerular (JG) granular cells in the distal part of the renal afferent arterioles. The rate of secretion of renin from JG cells is one of the main determinants of the overall activity of the renin-angiotensin system, and is the most well regulated parameter of all constituents of that system. At least three cellular messengers are involved in the intracellular control of renin secretion. Intracellular calcium is an inhibitory second messenger and is increased after exposure of the JG cells to vasoconstrictors such as angiotensin II, a1-adrenergic agonists or endothelin [1]. Cyclic AMP stimulates the secretory process and is involved in the stimulation of renin secretion seen after exposure to vasodilator hormones coupled to activation of adenylyl cyclase (dopamine [2], b-adrenergic agonists [3], prostaglandin E2, prostaglandin I2 and adrenomedullin [4]). Cyclic GMP may inhibit or stimulate renin secretion depending on which of several pathways dominate [5]. Many of the cellular and subcellular processes involved in the renin secretory control are not well understood.