We investigated whether osmotic stress would activate specific ion channels in bovine aortic endothelial cells (BAECs). In isotonic medium (290 mosmol/kgH2O), cell-attached patch recordings contained both 165-pS K+ channels activated by depolarization and 40-pS K+ channels activated by 200 nM bradykinin. These inwardly rectifying K+ channels were activated by raising “cytoplasmic” Ca2+ in inside-out patches. BAEC exposed to hypotonic bath (220 mosmol/kg) exhibited a 20% decrease in intracellular K+ content within 5 min. Cell-attached patches revealed biphasic K+ channel activation with hypotonic exposure; initial activation of 165- and 40-pS K+ channels (1–3 min) was followed by a delayed but sustained reactivation of both K+ channels (> 5 min). The delayed reactivation phase was dependent on the presence of external Ca2+ and was attenuated by 10 microM gadolinium. A 28-pS nonselective cation channel (NSCC), which conducted inward Ca2+ current, was also detected during hypotonic exposure. This NSCC was stimulated by hyperpolarization and was blocked by 10 microM gadolinium. In BAEC 1) hypotonic exposure activates Ca(2+)-dependent, 165- and 40-pS K+ channels biphasically; 2) the initial phase is independent of external Ca2+, while the delayed phase requires external Ca2+; and 3) Ca(2+)-permeable, 28-pS NSCCs stimulated by membrane hyperpolarization provide a pathway for external Ca2+ influx.
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