The relationship between acetylcholine-evoked Ca(2+)-dependent current and the Ca2+ concentrations in the cytosol and the lumen of the endoplasmic reticulum in pancreatic acinar cells.
In a study of isolated mouse pancreatic acinar cells, we used the patch-clamp whole-cell recording configuration to monitor the Ca(2+)-dependent inward ionic current and simultaneously measured the Ca2+ concentration in either the cytosol ([Ca2+]i) or the lumen of the endoplasmic reticulum ([Ca2+]Lu), using appropriate Ca(2+)-sensitive fluorescent probes. A high concentration of acetylcholine (ACh, 10 microM) evoked an increase in [Ca2+]i, which resulted in the activation of Ca(2+)-dependent inward current. Continued ACh application for several minutes led to a marked reduction in both the current and the [Ca2+]i response and after about 4-10 min of sustained ACh stimulation, the inward current response had disappeared and [Ca2+]i was back to the pre-stimulation level. Repeated stimulation with shorter pulses of ACh (10 microM) resulted in responses of declining magnitude both in terms of inward current and [Ca2+]i rises. The ACh-activated inward current was entirely dependent on the elevation of [Ca2+]i, but at a relatively high [Ca2+]i the current was saturated. ACh caused a rapid release of Ca2+ from the lumen of the endoplasmic reticulum and after discontinuation of stimulation, [Ca2+]Lu was only very slowly (10-15 min) fully restored to the pre-stimulation level. Repeated applications of ACh did not change the relationships between the Ca(2+)-dependent current and [Ca2+]i or the current and [Ca2+]Lu. When [Ca2+]Lu was greater than 100 microM, the ACh-evoked Ca2+ release from the store was so large that the current response was initially saturated. We conclude that the ACh-evoked current response essentially depends on the release of stored Ca2+. Desensitization is mainly due to the relatively slow reloading of the intracellular stores with Ca2+.
Park
M K
MK
Physiological Laboratory, University of Liverpool, UK.
Tepikin
A V
AV
Petersen
O H
OH
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D004553:Electric Conductivity; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D051379:Mice; D009994:Osmolar Concentration; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques
D000109:Acetylcholine; D002118:Calcium