Cs+ inhibits spontaneous Ca2+ release from sarcoplasmic reticulum of skinned cardiac myocytes.
The effect of Cs+ on the function of the cardiac sarcoplasmic reticulum (SR) has been investigated in skinned cardiac myocytes. Isolated rat ventricular myocytes were permeabilized using saponin and then perfused with a solution containing 150 nmol/l Ca2+ and 10 micromol/l fura 2. Fura 2 fluorescence from the skinned cell was monitored to assess SR Ca2+ release. The frequency of spontaneous Ca2+ release from the SR decreased when K+ in the bathing solution was completely replaced with Cs+. Cs+ had little effect on the amplitude of spontaneous release but prolonged both the rise time and decay time. The SR Ca2+ content, assessed by application of caffeine, was reduced in the Cs+ solution. Cyclopiazonic acid produced effects similar to those of Cs+. Extracellular Cs+ (20 mmol/l) increased the amplitude of the Ca2+ transient and the SR Ca2+ content in intact field-stimulated cells but had little effect on the Ca2+ transient when the amplitude and duration of depolarization were kept constant using voltage clamp. These data suggest that Cs+ slows Ca2+ movement across the SR membrane, possibly by blocking the SR K+ channel, but has additional effects in intact cells that overcome its inhibitory effects on the SR.
Department of Physiology, University of Leeds, Leeds LS2 9NQ, United Kingdom.
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Kawai
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Hussain
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Orchard
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002586:Cesium / Q000494:pharmacology*; D005260:Female; D006352:Heart Ventricles; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014665:Vasodilator Agents / Q000494:pharmacology
D007211:Indoles; D014665:Vasodilator Agents; D002586:Cesium; D002110:Caffeine; D011188:Potassium; D002118:Calcium; C000543:cyclopiazonic acid