Voltage-dependent InsP3- insensitive calcium channels in membranes of pancreatic endoplasmic reticulum vesicles

Abstract

Stimulus-secretion coupling in exocrine glands involves Ca2+ release from intracellular stores. In endoplasmic reticulum vesicle preparations from rat exocrine pancreas, an inositol 1,4,5-trisphosphate(InsP3)-sensitive, as well as an InsP3-insensitive, Ca2+ pool has been characterized. But Ca2+ channels in the endoplasmic reticulum of rat exocrine pancreas have not been demonstrated at the level of single-channel current. We have now used the patch-clamp technique on endoplasmic reticulum vesicles fused by means of the dehydration-rehydration method. In excised patches, single Ba2(+)- and Ca2(+)-selective channels were recorded. The channel activity was markedly voltage-dependent. Caffeine increased channel open-state probability, whereas ruthenium red and Cd2+ blocked single-channel currents. Ryanodine, nifedipine and heparin had no effect on channel activity. The channel activity was not dependent on the free Ca2+ concentration, the presence of InsP3, or pH. We conclude that this calcium channel mediates Ca2+ release from an intracellular store through an InsP3-insensitive mechanism.

The effect of caffeine on prostaglandin output from the guinea‐pig uterus

“…Thus it is unlikely that caffeine is stimulating uterine prostaglandin synthesis by acting on a ryanodine Type 3 receptor. Caffeine-sensitive calcium stores have been reported as being present in adrenal chromaffin cells (Burgoyne et al, 1989), liver (Shoshan-Barmatz, 1990) and pancreas (Schmid et al, 1990). The receptor type involved in the chromaffin cells and liver may be one of the three main ryanodine types.…”

Caffeine-Induced Ca 2+ Transients and Exocytosis in Paramecium Cells. A Correlated Ca 2+ Imaging and Quenched-Flow/Freeze-Fracture Analysis

“…However, not all of these stores are sensitive to caffeine (Schmid et al, 1990;Berridge, 1993;Cheek & Barry, 1993;Lynn & Gillespie, 1995). After detection of cyclic adenosine-diphosphoribose (cADPR) as a physiological activator of ryanodine-sensitive Ca 2+ pools in some secretory cells (Galione, 1994;Lee, 1994), some of the stores proved less or not sensitive to caffeine (Galione, Lee & Busa, 1991;Buck, Rakow & Shen, 1992;Verma et al, 1996), while some caffeine-activated stores were insensitive to cADPR (Meissner, 1994).…”

Caffeine causes glycerophosphorylcholine accumulation through ryanodine-inhibitable increase of cellular calcium and activation of phospholipase A2 in cultured MDCK cells

“…Zacchetti et al (1991) have suggested that PC12 cells express two distinct intracellular Ca 2 + channels, i. e. the receptor for c a ffeine-ryanodine and the inositol 1,4,5-triphosphate which appear to be colocalized. These suggestions are unlikely since caffeine-sensitive Ca 2 + channel is not a ffected by ryanodine in pancreatic endo-plasmic reticulum vesicles (Schmid et al, 1990). In the M D C K cells, caffeine-induced Ca 2 + release was inhibited b y ryanodine, demonstrating that Ca 2 + channel modulated by caffeine are sensitive to the ryanodine.…”

“…A similar result has been observed by diacylglycerol in HeLa cells in culture (Utal e t a l., 1991). Moreover, (Schmid et al, 1990;Stauderman and Murawsky, 1991;Pelech and Vance, 1989;Wakui et a l., 1990;Zacchetti et al, 1991). Figures 5 and 6).…”

“…These results demonstrate that caffeine increases MDCK [Ca 2 + ] i concentration and it is involved in the PLA 2 activity. C a ffeine and ryanodine are known to selectively influence the process of Ca 2 + release in a variety of cells from intracellular calcium pool (Iino et al, 1988;Malgaroli et al, 1990;Schmid et al, 1990;Stauderman and Murawsky, 1991;Wakui et al, 1990;Zacchetti e t a l., 1991). Biochemical, pharmacological and genetic studies have demonstrated the functional properties of C a 2 + channel modulated by these compounds.…”