Thiopental does not alter Ca2+ uptake by cardiac sarcoplasmic reticulum.

The effect of thiopental on Ca2+ uptake by cardiac sarcoplasmic reticulum (SR) isolated from the rabbit was examined to clarify the role of the sarcoplasmic reticulum in the negative inotropic action of thiopental. Thiopental, from 0 to 378 microM, did not alter the rate of Ca2+ uptake by the SR. We also compared the ATP dependence of Ca2+ uptake in the presence and absence of 284 microM thiopental. The Km for ATP and the Vmax of Ca+ uptake were unaffected by thiopental. It is concluded that thiopental does not alter Ca2+ uptake by the SR and that the negative inotropic effects of thiopental occur at other sites in the myocardial cell.