Voltage dependence of bovine pulmonary artery endothelial cell function*1

Vascular mediator synthesis in endothelial cells is Ca 2+ sensitive. Bradykinin increases [Ca 2+ ] i by releasing it from intracellular stores and by increasing influx across the plasmalemma. The latter is believed to occur through receptor-operated channels. Although gating of these plasmalemmal channels is voltage-insensitive, we hypothesized that Ca 2+ influx would still be dependent on the Ca 2+ electrochemical gradient and relative cation permeability. Using cultured bovine pulmonary endothelial cells we therefore measured: membrane voltage ( E m ) in single cells using the “tight seal” whole cell recording technique, Ca 2+ i in endothelial cell monolayers using fura-2, and arachidonic acid (AA) release using 3 H-AA prior to and following exposure to bradykinin at different [K + ] 0 . Our data indicate that the resting membrane potential of these cells is at least −67 mV in physiological saline and that the background resting membrane properties can be described with a ( P Na P K ) ratio of ∼0.027–0.040. Varying [K + ] 0 is shown to be an effective means for altering and controlling membrane potential and thus the calcium electrochemical gradient. Increases in [K + ] 0 lead to a concentration-dependent decrease in the magnitude of the Ca 2+ transient and in the relative amount of arachidonic acid released following exposure to bradykinin suggesting that Ca 2+ influx through the plasmalemma and AA release are regulated by the Ca 2+ electrochemical gradient. In addition, a simple theoretical membrane conductance model is presented which is able to reconcile the wide range in apparent resting membrane potentials which have been reported for endothelial cells.