Mechanisms that regulate [Ca2+]i following depolarization in rat systemic arterial smooth muscle cells.
1. We have used the patch-clamp technique in combination with fluorimetric recording to study the mechanisms that regulate intracellular Ca2+, [Ca2+]i, following depolarization in cells isolated from the rat femoral artery. 2. Depolarization to 0 mV from a holding potential of -70 mV increased [Ca2+]i. Little Ca2+ release from sarcoplasmic reticulum, SR, was detected during depolarization since application of 30 microM ryanodine, a Ca2+-release inhibitor, had no significant effect on total Ca2+ buffering power. 3. Upon repolarization to -70 mV, 7 out of 13 cells showed three phases of Ca2+ removal; an initial rapid first phase, a slow second phase, and a faster third phase. Six cells, in which Ca2+ recovered quickly, lacked the third phase. The third phase was also absent in cells treated with a SR Ca2+-pump inhibitor, cyclopiazonic acid. 4. The peak first-phase Ca2+ removal rate observed upon repolarization to -70 mV was significantly reduced in cells treated with a mitochondrial Ca2+ uptake inhibitor, carbonyl cyanide m-chlorophenylhydrazone. However, an ATP-synthase inhibitor, oligomycin B, had no significant effect. 5. The Ca2+ removal rate was little affected by clamping the cell at +120 mV rather than -70 mV, suggesting that Ca2+ removal processes are largely voltage independent. Also, little inward current was associated with Ca2+ clearance, indicating that Ca2+ removal does not involve an electrogenic process. 6. Our results suggest that Ca2+-induced Ca2+ release contributes little to the elevation of Ca2+ in these cells. The SR Ca2+ pump may contribute to Ca2+ removal over a low [Ca2+]i range in cells where [Ca2+]i remains high for long enough, while mitochondrial Ca2+ uptake may be important when [Ca2+]i is high.
Kamishima
T
T
Ion Channel Group, Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, Leicester LE1 9HN, UK. tk21@le.ac.uk
Davies
N W
NW
Standen
N B
NB
D000818:Animals; D001158:Arteries / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D005470:Fluorometry; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008931:Mitochondria, Muscle / Q000201:enzymology / Q000648:ultrastructure; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure
D015220:Calcium Channels; D007476:Ionophores; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000252:Calcium-Transporting ATPases; D002118:Calcium