Voltage-dependent InsP3-insensitive calcium channels in membranes of pancreatic endoplasmic reticulum vesicles.
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.
Max-Planck-Institut für Biophysik, Frankfurt (Main), FRG.
A
A
Schmid
M
M
Dehlinger-Kremer
I
I
Schulz
H
H
Gögelein
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008561:Membrane Fusion; D008564:Membrane Potentials / Q000187:drug effects; D009532:Nickel / Q000494:pharmacology; D010179:Pancreas / Q000502:physiology*; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology
D015220:Calcium Channels; D002104:Cadmium; D012430:Ruthenium Red; D002110:Caffeine; D009532:Nickel; D015544:Inositol 1,4,5-Trisphosphate