The effect of menadione on sarcoplasmic reticulum Ca2+ and contractions of single guinea-pig cardiomyocytes.
We investigated the effect of 2-methyl-1,4-naphtoquinone (Menadione) on sarcoplasmic reticulum (SR) Ca2+ content and electrically stimulated contractions (ESCs) of single isolated myocytes of guinea-pig ventricular myocardium. The contractures initiated by means of microinjections of caffeine into the close vicinity of the cell were used as an indirect index of the SR Ca2+ content. Superfusion of the cells for 45 min with Menadione resulted in gradual disappearance of contractile responses to caffeine, prolongation of time to peak amplitude of ESCs by 48 +/- 15% and complete inhibition of postrest and postextrasystolic potentiation. These results are consistent with those of Floreani and Carpenedo (7) who found that Menadione strongly inhibits the SR Ca2+ ATPase. Despite depletion of the SR Ca2+ the amplitude of ESCs did not change which suggests that contractions were initiated in the cells treated with Menadione by Ca2+ derived from the sources other than the SR.
Lewartowski
B
B
Department of Clinical Physiology, Medical Center of Postgraduate Education, Warsaw, Poland.
Zdanowski
K
K
Wolska
B M
BM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D004558:Electric Stimulation; D006168:Guinea Pigs; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D012146:Rest; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013599:Systole; D014812:Vitamin K / Q000494:pharmacology*
D014812:Vitamin K; D002118:Calcium