Inositol 1,4,5-trisphosphate releases Ca2+from a nonmitochondrial store site in permeabilized rat cortical kidney cells

Abstract

We have recently shown that inositol 1,4,5-trisphosphate (IP3) releases Ca2+ from the endoplasmic reticulum of pancreatic acinar cells and suggested that IP3 may function as a second messenger of hormonal receptors to mobilize Ca2+ from intracellular stores (Streb et al, 1983, Streb et al, 1984). In rat kidney cortical tubules and microdissected mouse proximal tubules, an increased turnover of polyphosphoinositide metabolism following hormonal stimulation with angiotensin II-amide and phenylephrine has been reported (Wirthensohn et al, 1984; Wirthensohn et al, 1985). This suggests that IP3, one of their hydrolysis products, increases during hormonal stimulation. We therefore investigated the effect of angiotensin II-amide and IP3 on intracellular Ca2 stores in saponin-treated cells and homogenate from rat kidney cortex. Saponin-treated isolated cortical kidney cells or homogenate was incubated in a high K+ buffer in the presence of MgATP and respiratory substrates. Ca2+ uptake was determined by measuring the free Ca2+ concentration of the surrounding medium with a Ca2+ specific macroelectrode. Addition of cells or homogenate to the incubation medium resulted in a decrease of the medium free Ca2+ concentration until a steady-state concentration of 5.7 +/- 0.2 X 10(-7) mole/l was obtained. In the presence of mitochondrial inhibitors Ca2+ uptake rate was reduced, whereas the steady-state concentration was unchanged. In contrast, in the presence of the CA2+-ATPase inhibitor vanadate mitochondrial uptake proceeded at the same rate as the control, but the steady-state concentration was higher (6.9 +/- 0.2 X 10(-7) mole/l).(ABSTRACT TRUNCATED AT 250 WORDS)

H+/Ca2+ exchange in rabbit renal cortical endosomes

“…A nonmitochondrial Ca z+ storage site in rat renal cortical cells has been reported, which evidently responds to IP3 by releasing Ca 2+ (Th6venod et al, 1986). In our studies, the inability of IP3 to change the Ca 2+ content of rabbit renal cortical endosomes might indicate the absence of an IP3 receptor on these membranes.…”

Angiotensin II Actions in the Rabbit Proximal Tubule

“…An active PLC pathway has been suggested to exist in the proximal tubule based on observations of ,2P incorporation into phosphatidylcholine (PC) and phosphoinositol (PI) [16], and IPr induced [Ca2+]i release from nonmitochondrial pools [17]. Th6venod et al [ 17] found that ICC M Angll-amide mimicked the IP3-induced [Ca2+], release; and in addition. Wirthensohn and Guder [16] showed that 10"5 M Angll increased 32P incorporation into PC and PI.…”

“…Angll activates phospholipase C (PLC) as a major signaling pathway to re lease inositol-1,4.5-trisphosphate (IPs) and diacylglycérol (DAG), which in turn elevate cytosolic Ca2+ ([Ca2'],) and activate protein kinase C. respectively [13][14][15]. An active PLC pathway has been suggested to exist in the proximal tubule based on observations of ,2P incorporation into phosphatidylcholine (PC) and phosphoinositol (PI) [16], and IPr induced [Ca2+]i release from nonmitochondrial pools [17]. Th6venod et al [ 17] found that ICC M Angll-amide mimicked the IP3-induced [Ca2+], release; and in addition.…”

Renal Tubular Transport of Calcium

“…They concluded that, in the absence of a functioning plasma membrane, steadystate levels of cytosolic calcium are regulated by a nonmitochondrial pool, probably in the endoplasmic reticulum. Only when cells are loaded with unphysiologically high amounts of calcium, exceeding the uptake capacity of the endoplasmic reticulum, do mitochondria assume a major role in buffering cytosolic calcium (42,210 (42,103,210), serving as the intracellular messenger for various hormonal stimuli, similar to the role described in other systems (12,166).…”