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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.

Vascular mediator synthesis in endothelial cells is Ca2+ sensitive. Bradykinin increases [Ca2+]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 Ca2+ influx would still be dependent on the Ca2+ electrochemical gradient and relative cation permeability. Using cultured bovine pulmonary endothelial cells we therefore measured: membrane voltage (Em) in single cells using the "tight seal" whole cell recording technique, Ca2+i in endothelial cell monolayers using fura-2, and arachidonic acid (AA) release using 3H-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 (PNa/PK) ratio of approximately 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 Ca2+ transient and in the relative amount of arachidonic acid released following exposure to bradykinin suggesting that Ca2+ influx through the plasmalemma and AA release are regulated by the Ca2+ 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.