Effect of thiopental on Ca2+ release from sarcoplasmic reticulum in intact myocardium.
BACKGROUND
While thiopental is known to inhibit the myocardial transsarcolemmal influx of Ca2+, the effect of thiopental on sarcoplasmic reticular Ca2+ release has not been characterized.


METHODS
Isolated papillary muscles of rabbits were used. We measured postrest contractions to assess the Ca2+ release by sarcoplasmic reticulum in response to electrical stimulation. Contractures induced by rapid cooling were used as an index of Ca2+ content of sarcoplasmic reticulum. The effect of thiopental on the availability of extracellularly derived Ca2+ was evaluated from measurements of contractions at 0.1 Hz in the presence of 1 microM ryanodine.


RESULTS
Thiopental sodium (10, 20, and 30 mg/l; 38, 76, and 113 microM) inhibited the postrest contraction but not the contracture induced by rapid cooling. In the presence ryanodine, thiopental inhibited the postrest contraction elicited after 10 s of rest after 2-Hz stimulation much less than the steady-state contraction at 0.1 Hz (beat interval 10 s). Thiopental inhibited the postrest contraction (no ryanodine present) more strongly than did Ni2+ (an inhibitor of the transsarcolemmal Ca2+ influx) when the contraction at 0.1 Hz in the presence of ryanodine was inhibited to the same extent.


CONCLUSIONS
These results suggest that thiopental decreases sarcoplasmic reticulum Ca2+ release induced by electrical stimulation and inhibits the ryanodine-induced efflux of sarcoplasmic reticulum Ca2+.
Komai
H
H
Department of Anesthesiology, University of Wisconsin, Madison.
Rusy
B F
BF
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D009532:Nickel / Q000494:pharmacology; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D013874:Thiopental / Q000494:pharmacology*
D012433:Ryanodine; D009532:Nickel; D013874:Thiopental; D002118:Calcium