Premium
Mechanisms that regulate [Ca 2+ ] i following depolarization in rat systemic arterial smooth muscle cells
Author(s) -
Kamishima T.,
Davies N. W.,
Standen N. B.
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.t01-2-00285.x
Subject(s) - depolarization , cyclopiazonic acid , repolarization , biophysics , chemistry , ryanodine receptor , calcium , intracellular , membrane potential , oligomycin , endoplasmic reticulum , medicine , biochemistry , electrophysiology , biology , organic chemistry , atpase , enzyme
1 We have used the patch‐clamp technique in combination with fluorimetric recording to study the mechanisms that regulate intracellular Ca 2+ , [Ca 2+ ] i , following depolarization in cells isolated from the rat femoral artery. 2 Depolarization to 0 mV from a holding potential of −70 mV increased [Ca 2+ ] i . Little Ca 2+ release from sarcoplasmic reticulum, SR, was detected during depolarization since application of 30 μM ryanodine, a Ca 2+ ‐release inhibitor, had no significant effect on total Ca 2+ buffering power. 3 Upon repolarization to −70 mV, 7 out of 13 cells showed three phases of Ca 2+ removal; an initial rapid first phase, a slow second phase, and a faster third phase. Six cells, in which Ca 2+ recovered quickly, lacked the third phase. The third phase was also absent in cells treated with a SR Ca 2+ ‐pump inhibitor, cyclopiazonic acid. 4 The peak first‐phase Ca 2+ removal rate observed upon repolarization to −70 mV was significantly reduced in cells treated with a mitochondrial Ca 2+ uptake inhibitor, carbonyl cyanide m ‐chlorophenylhydrazone. However, an ATP‐synthase inhibitor, oligomycin B, had no significant effect. 5 The Ca 2+ removal rate was little affected by clamping the cell at +120 mV rather than −70 mV, suggesting that Ca 2+ removal processes are largely voltage independent. Also, little inward current was associated with Ca 2+ clearance, indicating that Ca 2+ removal does not involve an electrogenic process. 6 Our results suggest that Ca 2+ ‐induced Ca 2+ release contributes little to the elevation of Ca 2+ in these cells. The SR Ca 2+ pump may contribute to Ca 2+ removal over a low [Ca 2+ ] i range in cells where [Ca 2+ ] i remains high for long enough, while mitochondrial Ca 2+ uptake may be important when [Ca 2+ ] i is high.