Further studies on properties of renin granules isolated from rat kidney cortex.

Abstract

The properties of renin granules isolated from rat renal cortex were studied. Renin granules were thermolabile since in 10 min at 0 degrees C twice as much renin was released as at +37 degrees C. Addition of Ca++ (10(-6) M - 10(-2) M) did not affect the spontaneous release at +37 degrees C, pH 6.5, during 10 or 30 min incubation. However, when pH was elevated to above 7, renin release was significantly increased by Ca++ (10(-3) M). Additions of various amounts of KCl, NaCl or MgCl2, which increased the osmolality less than 20 mOsm/kg, did not affect the stability of the renin granules. Mg-ATP (0.5 and 5 mM) as well as Mg-GTP (5 mM) stabilized renin granules at +37 degrees C, pH 6.5, but the corresponding nitrogen analogues Mg-AMP-PNP and Mg-GMP-PNP (0.5 and 5 mM) were not effective. Neither did Mg-AMP (5 mM) nor ATP (5 mM) without Mg++ affect the renin release. No stabilization was observed by Mg-ATP and Mg-GTP in the purified granule preparations. The results suggest the importance of the cleavage of the terminal phosphate in the stabilization process. When the granules prepared at 300 mOsm/kg were first kept at hyperosmotic medium (range 300-1650 mOsm/kg) and then moved back to 300 mOsm/kg, the granules tend to lyse the more the greater was the reduction of the osmolality. The granules were more stable in isotonic sucrose than in isotonic ionic medium.