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Effect of atropine, ouabain, antimycin A, and A23187 on "trigger Ca2+ pool" in exocrine pancreas

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Stolze,  Hans H.
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Schulz,  Irene
Department of Physiology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Stolze, H. H., & Schulz, I. (1980). Effect of atropine, ouabain, antimycin A, and A23187 on "trigger Ca2+ pool" in exocrine pancreas. American Journal of Physiology-Gastrointestinal and Liver Physiology, 238(4), G338-G348. doi:10.1152/ajpgi.1980.238.4.G338.


Cite as: https://hdl.handle.net/21.11116/0000-0008-3E86-C
Abstract
45Ca2+ fluxes have been analyzed in dispersed acinar cells prepared from rat pancreas. Sudden addition of carbamylcholine (CCh) to 45Ca2+-preloaded acinar cells at quasi-steady state for 45Ca2+ resulted in a quick 45Ca2+ release followed by a slower 45Ca2+ reuptake with net accumulation of 45Ca2+. Subsequent sudden addition of atropine caused a further transient increase in cellular 45Ca2+ followed by a slow decrease to a steady-state value. 45Ca2+ release could not be evoked a second time by pancreozymin when prestimulated with CCh. However, if CCh stimulation was abolished by an interposed step of atropine, restimulation by cholecystokinin-pancreozymin was possible. Addition of A23187 or antimycin A to cells induced a fast decrease in cellular 45Ca2+. This effect was not additive to the CCh effect. In ouabain-pretreated cells, the CCh-induced sudden loss of cellular 45Ca2+ was blocked by 60%. The following slow reuptake of 45Ca2+ was blocked completely. Subsequent addition of atropine caused a fast uptake of cellular 45Ca2+ with no secondary decline. The data are consistent with the following model: acetylcholine releases Ca2+ from a cellular "trigger pool" into the cytosol located in or near the cell membrane. Then Ca2+ is extruded from the cell via Ca2+ pumps partly by a Na+-dependent Ca2+ transport system (quick phase of 45Ca2+ release). Subsequently, due to increased Ca2+ permeability of the plasma membrane as induced by acetylcholine, Ca2+ influx occurs and Ca2+ is taken up from the cytosol into intracellular Ca2+ pools (slow 45Ca2+ reuptake phase). Atropine causes refilling of the trigger Ca2+ pool and return of the increased Ca2+ permeability of the plasma membrane back to the unstimulated state.