Angiotensin II, vasopressin and GTP[γ-S] inhibit inward-rectifying K+ channels in porcine cerebral capillary endothelial cells

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Abstract
Cerebral capillaries from porcine brain were isolated. and endothelial cells were grown in primary culture. The whole-cell tight seal patch-clamp method was applied to freshly isolated single endothelial cells, and cells which were held in culture up to one week. With high K+ solution in the patch pipette and in the bath we observed inward-rectifying K+ currents, showing a time-dependent decay in part of the experiments. Ba2+ (1–10mm) in the bath blocked this current, whereas outside tetraethylammonium (10mm) decreased the peak current but increased the steady-state current. Addition of 1 μm of angiotensin II or of arginine-vasopressin to the extracellular side caused a time-dependent inhibition of the inward-rectifying K+ current in part of the experiments. Addition of 100 μm GTP[γ-S] to the patch pipette blocked the K+ inward rectifier. In cell-attached membrane patches two types of single inward-rectifying K+ channels were observed, with single channel conductances of 7 and 35 pS. Cell-attached patches were also obtained at the antiluminal membrane of intact isolated cerebral capillaries. Only one type of K+ channel withg=30 pS was recorded. In conclusion, inwardly rectifying K+ channels, which can be inhibited by extracellular angiotensin II and arginine-vasopressin, are present in cerebral capillary endothelial cells. The inhibition of this K+ conductance by GTP[γ-S] indicates that G-proteins are involved in channel regulation. It is suggested that angiotensin II and vasopressin regulate K+ transport across the blood-brain barrier, mediating their effects via G-proteins.