Voltage dependence of bovine pulmonary artery endothelial cell function

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.