OSMOTICALLY SENSITIVE RENIN RELEASE FROM PERMEABILIZED JUXTAGLOMERULAR CELLS

Renin secretion from juxtaglomerular (JG) cells is sensitive to extern al osmolality in a way that has been suggested to depend either on cel lular volume or on effects on secretory granules. To distinguish betwe en these possibilities, a technique for permeabilization of JG cell me mbranes was developed. Rat glomeruli with attached JG cells were isola ted and permeabilized by 20 muM digitonin for 12 min and followed by c ontinuous exposure to 2 muM digitonin. Experiments on proximal tubules showed that cellular volume was unaffected by changes in external suc rose concentration after a similar permeabilization procedure. With pe rmeabilized JG cells the following changes in osmolality were tested ( in mM sucrose): +90 (n = 6), +60 (n = 5), +30 (n = 6), +15 (n = 6), -1 5 (n = 5), -30 (n = 6), -60 (n = 6), and -90 (n = 6). With nonpermeabi lized 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 os molality caused inhibition of renin release, whereas decreases stimula ted secretion. Within +/-10% variations in osmolality there were no di fferences between the responses in permeabilized and intact cells, whe reas the responses with larger changes were less in the permeabilized cells. Increase or decrease in urea concentration by 30 mM did not aff ect renin release. Thus water fluxes can influence renin release by a mechanism that is independent of cell volume.