INTRACELLULAR CALCIUM-RELEASE IS MORE EFFICIENT THAN CALCIUM INFLUX IN STIMULATING MITOCHONDRIAL NAD(P)H FORMATION IN ADRENAL GLOMERULOSA CELLS

We compared the effect on mitochondrial NAD(P)H formation of calcium r elease from intracellular stores with that of calcium influx from the extracellular space. Simultaneous measurements of cytoplasmic free cal cium ion concentration and mitochondrial NAD(P)H were performed on fur a-PE3-loaded single rat adrenal glomerulosa cells. The effects of equi potent stimuli in terms of the evoked Ca2+ response were compared. Ang iotensin II (AII; 1 nM) induced a higher amplitude NAD(P)H response th an K+ (5.6-7.6 mM). Vasopressin (1 mu M) also induced a greater initia l NAD(P)H formation than K+, although the Ca2+ signal evoked by the tw o agonists had similar amplitude. To examine the effect of Ca2+ releas e from internal stores we applied AII in Ca2+-free medium. We compared the effect on NAD(P)H formation of Ca2+ release with Ca2+ influx indu ced by K+, and with capacitative Ca2+ influx induced by AII. NAD(P)H f ormation in response to Ca2+ release was greater than that induced by Ca2+ influx, irrespective of whether induced by K+ or AII. Our results indicate that Ca2+, presumably released in the vicinity of mitochondr ia, activates mitochondrial dehydrogenases more efficiently than Ca2entering through the plasma membrane. These data confirm the biologica l significance of previous observations showing that Ca2+ released fro m inositol 1,4,5-trisphosphate-sensitive internal stores increases mit ochondrial matrix [Ca2+] to a greater extent than extracellular Ca2+.