Ca 2+ Flux Through Voltage‐Gated Channels with Flow Cessation in Pulmonary Microvascular Endothelial Cells

Objective: To investigate the role of voltage‐gated Ca 2+ channels in Ca 2+ influx with flow cessation in flow‐adapted rat pulmonary microvascular endothelial cells. Methods: Cells were evaluated for mRNA and protein levels for major components of the voltage‐gated Ca 2+ channels. Ca 2+ influx with flow cessation and cell membrane potential were measured in real time with fluorescent dyes. Mibefradil and nifedipine were used as inhibitors of Ca 2+ channel activity. Results: Voltage‐gated Ca 2+ channel protein and mRNA for the T‐type channel were expressed at a relatively low level in endothelial cells cultured under static conditions and expression was induced significantly during flow adaptation. Flow‐adapted but not control cells showed Ca 2+ influx during flow cessation that was blocked by mibefradil but not by nifedipine. Ca 2+ influx also was blocked by cromakalim, a K ATP channel agonist. Cell membrane depolarization with flow cessation was unaffected by mibefradil. Conclusions: Rat pulmonary microvascular endothelial cells express T‐type voltage‐gated Ca 2+ channels that are induced during adaptation to flow and are responsible for Ca 2+ influx that occurs as a result of flow cessation‐mediated membrane depolarization.