Biomedical subjects
R L Stevenson
Publications and source records attributed to R L Stevenson.
Halothane decreases calcium channel antagonist binding to cardiac membranes.
The effect of halothane concentration on the binding of the calcium antagonist, [3H] nitrendipine (3HNTP), to rat and rabbit heart membranes was examined in vitro because it has been hypothesized that one mechanism by which halothane depresses cardiac contractility is by interfering with Ca2+ channel function. Membranes were incubated for 90 minutes in a closed system with 3HNTP and increasing concentrations of halothane. The amount of 3HNTP bound to membranes was quantified by radioligand binding technique and liquid scintillation counting. It was found in both the rat and rabbit cardiac membranes that halothane (0.4-2.0%) caused a dose-dependent decrease in specific 3HNTP binding (P less than 0.0001). The decrease in 3HNTP binding caused by halothane was also found to be reversible. These results indicate that halothane interferes with one property of the Ca2+ channel and suggest that this may be one possible mechanism for the negative inotropic action of halothane.
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.