Effect of membrane potential on cytosolic calcium of bovine aortic endothelial cells

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Abstract
The effect of bradykinin on membrane potential of cultured bovine aortic endothelial cells (BAECs) was estimated by measuring the uptake of the lipophilic cation, tetra[3H]phenylphosphonium ([3H]TPP+). Uptake of [3H]TPP+ was found to be 1) a function of extracellular K+ concentration, 2) sensitive to valinomycin, and 3) decreased by the K+ channel inhibitor, Ba2+, suggesting that the uptake of [3H]TPP+ responds to changes in membrane potential of the BAEC. Bradykinin (50 nM) produced an increase in [3H]TPP+ uptake in low K+ buffer consistent with a bradykinin-induced membrane hyperpolarization. The effect of membrane depolarization with high K+ buffer on the bradykinin-stimulated changes in cytosolic Ca2+ was determined using the fluorescent Ca2+ indicator, fura-2. The results of these experiments demonstrated that both basal cytosolic Ca2+ and bradykinin-stimulated release of Ca2+ from internal stores were not affected by membrane depolarization. However, bradykinin-stimulated influx of Ca2+ from the extracellular space decreased with membrane depolarization in a manner consistent with the movement of Ca2+ through a channel.