A protein kinase G-sensitive channel mediates flow-induced Ca²⁺ entry into vascular endothelial cells

The hemodynamic force generated by blood flow is considered to be the physiologically most important stimulus for the release of nitric oxide (NO) and prostacyclin (PGI₂) from vascular endothelial cells (1). NO and PGI₂ then act on the underlying smooth muscle cells, causing vasodilation and thus lowering blood pressure (2, 3). One critical early event occurring in this flow-induced regulation of vascular tone is that blood flow induces Ca²⁺ entry into vascular endothelial cells, which in turn leads to the formation of NO (4, 5). Here we report a mechanosensitive Ca²⁺-permeable channel in vascular endothelial cells. The activity of the channel was inhibited by 8- Br-cGMP, a membrane-permeant activator of protein kinase G (PKG), in cell- attached membrane patches. The inhibition could be reversed by PKG inhibitor KT5823 or H-8. A direct application of active PKG in inside-out patches blocked the channel activity. Gd³⁺, Ni²⁺, or SK and F-96365 also inhibited the channel activity. A study of fluorescent Ca²⁺ entry revealed a striking pharmacological similarity between the Ca²⁺ entry elicited by flow and the mechanosensitive Ca²⁺-permeable channel we identified, suggesting that this channel is the primary pathway mediating flow-induced Ca²⁺ entry into vascular endothelial cells.