The effect of thapsigargin on sarcoplasmic reticulum Ca2+ content and contractions in single myocytes of guinea-pig heart.
Contractures initiated by 1 s superfusion of single myocytes of guinea-pig heart with 10 mM caffeine were used as a relative index of the SR Ca2+ content. Thapsigargin (Tg) in concentration 2 x 10(-7) M completely blocked Ca2+ uptake during electrical stimulation by the SR from which Ca2+ has been previously depleted by caffeine. Tg did not affect the SR Ca2+ content in the resting myocytes and did not block release of the SR Ca2+ during electrically stimulated contractions (ESCs). It is concluded that in guinea-pig myocytes Tg affects SR Ca2+ by selective blocking the SR Ca2+ uptake. The amplitude of steady state ESCs dropped to 68 +/- 5.4% (S.D., n = 20) of that of the pre-Tg control. Time to peak contraction increased from 454 +/- 82.4 ms to 820 +/- 157.4 ms and time of relaxation increased from 368 +/- 90.8 ms to 474 +/- 87 ms after the SR Ca2+ has been depleted by Tg. Rest decay of contractions, post-extrasystolic potentiation and post-rest potentiation were inhibited.
Lewartowski
B
B
Department of Clinical Physiology, Medical Centre of Postgraduate Education, Warsaw, Poland.
Wolska
B M
BM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D004558:Electric Stimulation; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D013729:Terpenes; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium