Direct demonstration of exocytosis and endocytosis in single mouse juxtaglomerular cells.

Abstract

The rate of renin secretion from renal juxtaglomerular (JG) cells is the major determinant of the activity of the renin-angiotensin system. However, the mechanisms involved in the excretion and turnover of secretory granules in the JG cells remain obscure. Therefore, in the present study, the whole-cell patch-clamp technique was applied to single JG cells from the mouse kidney to measure changes in cell membrane capacitance (Cm) as an index of secretory activity. Resting JG cell Cm was stable, on average 3. 13+/-0.13 pF (SEM, n=106). In isotonic solutions, Cm was unaffected by [Cl-]i. Cm was consistently increased (7.0+/-1.3% and 7.2+/-3.1%) by intracellular cAMP (1 to 10 micromol/L). This effect was mimicked by extracellular application of the beta-agonist isoproterenol to the JG cells (9.4+/-3.1%). At 100 micromol/L, cAMP induced a paradoxical decrease in Cm of </=20%, which was mimicked by forskolin. Cell swelling induced by a 7% reduction in osmolality increased Cm with no significant additional effects to [Cl-]i and cAMP. cAMP increased whole-cell outward current 2- to 4-fold in all groups, but no correlation between changes in whole-cell currents and Cm existed. We conclude that the whole-cell patch-clamp method allows the study of exocytosis and endocytosis in JG cells. Renin release induced by the cAMP pathway and by cell swelling is exocytotic, and high-intracellular cAMP levels activate membrane retrieval mechanisms.