Osmotically sensitive renin release from permeabilized juxtaglomerular cells

Abstract

Renin secretion from juxtaglomerular (JG) cells is sensitive to external osmolality in a way that has been suggested to depend either on cellular volume or on effects on secretory granules. To distinguish between these possibilities, a technique for permeabilization of JG cell membranes was developed. Rat glomeruli with attached JG cells were isolated and permeabilized by 20 microM digitonin for 12 min and followed by continuous exposure to 2 microM digitonin. Experiments on proximal tubules showed that cellular volume was unaffected by changes in external sucrose concentration after a similar permeabilization procedure. With permeabilized JG cells the following changes in osmolality were tested (in mM sucrose): +90 (n = 6), +60 (n = 5), +30 (n = 6), +15 (n = 6), -15 (n = 5), -30 (n = 6), -60 (n = 6), and -90 (n = 6). With nonpermeabilized cells similar experiments were done with changes of +90 (n = 7), +30 (n = 4), -30 (n = 4), and -90 (n = 6) mM sucrose. Increases in osmolality caused inhibition of renin release, whereas decreases stimulated secretion. Within +/- 10% variations in osmolality there were no differences between the responses in permeabilized and intact cells, whereas the responses with larger changes were less in the permeabilized cells. Increase or decrease in urea concentration by 30 mM did not affect renin release. Thus water fluxes can influence renin release by a mechanism that is independent of cell volume.