title: Calcium and osmotic stimulation in renin release from isolated rat glomeruli.
abstract: The effects of changes in osmolality and calcium concentration on renin release (RR) from isolated superfused rat glomeruli were studied. The undisturbed RR followed a first order fall with a half-time of about 100 min (n = 45). Changes in the osmolality between 270 and 350 mOsm/kg resulted in dose-dependent changes in the RR rates. Hypoosmotic treatment stimulated the RR transiently, whereas hyperosmotic treatment produced a sustained inhibition. The dose-response relationship was log-linear between 270 and 320 mOsm/kg. A decrease in osmolality of 20 mOsm/kg gave proportional increases in RR irrespectively of the RR rate preceding the stimulus. Removal of calcium stimulated the RR by 10 times (n = 5, p less than 0.001) and a subsequent decrease in osmolality of 20 mOsm/kg stimulated the RR proportionally to that observed in the series containing 2 mM calcium. A decrease in osmolality was able to stimulate RR (n = 5.5, p less than 0.05) even when the calcium concentration in the medium was simultaneously raised from 0 to 2 mM. A hyperosmotic Ringer (+ 300 mOsm/kg), inhibited RR to very low levels. A subsequent removal of external calcium was now unable to stimulate the release (n = 5.5). In a less hyperosmotic Ringer (+ 50 mOsm), the RR was inhibited, but a removal of external calcium now stimulated RR. It is suggested that the osmosensitivity of the RR process reflects a waterflux-driven fusion of secretory granules with the cell membrane, and that calcium affects an intragranular equilibrium between aggregated, osmotically inert granule content and dissolved, osmotically active granule content.
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D066298:In Vitro Techniques; D007678:Kidney Glomerulus / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D009995:Osmosis; D051381:Rats; D011919:Rats, Inbred Strains; D012083:Renin / Q000378:metabolism*; D013268:Stimulation, Chemical; D013395:Sucrose / Q000494:pharmacology; D013997:Time Factors
chemical_list: D013395:Sucrose; D012083:Renin; D002118:Calcium