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CALCIUM AND PANCREATIC SECRETION‐DYNAMICS OF SUBCELLULAR CALCIUM POOLS IN RESTING AND STIMULATED ACINAR CELLS
Author(s) -
CLEMENTE F.,
MELDOLESI J.
Publication year - 1975
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1975.tb06940.x
Subject(s) - calcium , intracellular , granule (geology) , secretagogue , acinar cell , microsome , biochemistry , secretion , biophysics , organelle , cell fractionation , chemistry , calcium in biology , biology , microbiology and biotechnology , membrane , in vitro , pancreas , paleontology , organic chemistry
1 Pulse‐chase experiments were carried out on pancreatic tissue lobules incubated in vitro , with 45 Ca as the tracer, in order to shed some light on the functional significance of the calcium pools associated with the various cell organelles of the acinar cell, especially in relation to stimulus‐secretion coupling. 2 The kinetics of tracer uptake and release which were observed in the intact lobules suggest the existence of a number of intracellular pools, whose rate of exchange is slower than that across the plasmalemma. 3 The various subcellular fractions accumulate the tracer in different amounts: some (rough microsomes and postmicrosomal supernatant) showed little radioactivity and some (smooth microsomes and zymogen granule membranes) were heavily labelled; mitochondria and zymogen granules showed intermediate values. 4 The fractions are heterogeneous also in relation to the time course of uptake and release of the tracer: in rough and smooth microsomes and, especially, in the postmicrosomal supernatant both rates were fast; zymogen granules and zymogen granule membranes showed slow rates of uptake and little release during chase; intermediate rates were found in mitochondria. 5 In agreement with previous findings we observed that in 45 Ca preloaded lobules, stimulation of secretion (brought about by the secretagogue polypeptide caerulein) results in an increase of the tracer release which seems to be due primarily to the rise of the intracellular concentration of free Ca 2+ and to the consequent increase of the transmembrane Ca 2+ efflux. Among the cell fractions isolated from stimulated lobules only the mitochondria exhibited a significantly lower 45 Ca level relative to the unstimulated controls. 6 It is concluded that, of the organelle‐bound calcium pools, that associated with the mitochondria might be involved in the regulation of the calcium‐dependent functions, including stimulus‐secretion coupling; the calcium associated with the zymogen granule content probably has a role in the architecture of the organelle and in the functionality of the pancreatic juice, while the calcium bound to the membrane of the granules might be concerned with the regulation of its permeability properties.