Effects of vanadate in cultured rat heart muscle cells. Vanadate transport, intracellular binding and vanadate-induced changes in beating and in active cation flux.

Cultured rat heart muscle cells have been used to study uptake and intracellular binding of Na483VO4 (vanadate), as well as the influence of vanadate on beating and 86Rb+ uptake of these cells. 1. Vanadate is taken up into cultured rat heart muscle cells in an energy-independent manner by a saturable transport system (Km approximately 60 microM, V approximately 200 pmol per mg protein per min at 37 degrees C). Analysis of intracellular binding of vanadate reveals a curved Scatchard plot indicating more than one binding site. Maximal binding amounts to 3 . 10(9) molecules of vanadate per cell. 2. Vanadate exerts a positive chronotropic and inotropic effect and increases automaticity. First effects can be seen at 1 . 10(-7) M Na3VO4. Concentrations higher than 1. 10(-3) M induce toxic effects (arrhythmias, fibrillation and stand-still of the cell). 3. Vanadate-induced alterations of beating is paralleled by a vanadate-induced stimulation of (86Rb+ + K+) uptake into the cells of up to 75%. Maximal stimulation is obtained at concentrations of 1 . 10(-4)--1 . 10(-3) M vanadate. The stimulation is thought to be due to an increased activity of (Na+ + K+)-ATPase, since it can be inhibited by ouabain. This result is in contrast to in vitro experiments with purified membrane preparations of (Na+ + K+)-ATPase of different organs, where an inhibition of (Na+ + K+)-ATPase by vanadate has been found. 4. The results indicate a possible role of vanadate as an endogenous regulator of active cation flux in heart tissue.