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Two Ca 2+ entry pathways mediate Ins P 3 ‐sensitive store refilling in guinea‐pig colonic smooth muscle
Author(s) -
McCarron John G.,
Flynn Elaine R. M.,
Bradley Karen N.,
Muir Thomas C.
Publication year - 2000
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2000.00113.x
Subject(s) - library science , neuroscience , medicine , psychology , computer science
1 Sarcolemma Ca 2+ influx, necessary for store refilling, was well maintained, over a wide range (‐70 to + 40 mV) of membrane voltages, in guinea‐pig single circular colonic smooth muscle cells, as indicated by the magnitude of Ins P 3 ‐evoked Ca 2+ transients. 2 This apparent voltage independence of store refilling was achieved by the activity of sarcolemma Ca 2+ channels some of which were voltage gated while others were not. At negative membrane potentials (e.g. ‐70 mV), Ca 2+ influx through channels which lacked voltage gating provided for store refilling while at positive membrane potentials (e.g. +40 mV) voltage‐gated Ca 2+ channels were largely responsible. 3 Sarcolemma voltage‐gated Ca 2+ currents were not activated following store depletion. 4 Removal of external Ca 2+ or the addition of the Ca 2+ channel blocker nimodipine (1 μM) inhibited store refilling, as assessed by the magnitude of Ins P 3 ‐evoked Ca 2+ transients, with little or no change in bulk average cytoplasmic Ca 2+ concentration. One hypothesis for these results is that the store may refill from a high subsarcolemma Ca 2+ gradient. 5 Influx via channels, some of which are voltage gated and others which lack voltage gating, may permit the establishment of a subsarcolemma Ca 2+ gradient. Store access to the gradient allows Ins P 3 ‐evoked Ca 2+ signalling to be maintained over a wide voltage range in colonic smooth muscle.