Lack of coupling between membrane stretching and pannexin-1 hemichannels.

We investigated whether pannexin-1, a carbenoxolone-sensitive hemichannel activated in erythrocytes by swelling, could be activated by swelling stress and contribute to swelling-activated chloride currents (I(Cl,swell)) in HEK-293 cells. We used ethidium bromide uptake as an index of pannexin-1 activation and I(C,swell) activation as an index of plasma membrane stretching. I(Cl,swell) activated by a hypotonic solution was reversible inhibited by carbenoxolone (IC(50) 98+/-5 microM). However, the hypotonic solution that activated I(Cl,swell) did not induce ethidium bromide uptake indicating that pannexin-1 was not activated by cell swelling. The mimetic peptide (10)panx1, a pannexin-1 antagonist, did not affect I(Cl,swell) activation but completely inhibited the ATP-induced ethidium bromide uptake coupled to P2X(7) receptors activation. We conclude that carbenoxolone directly inhibited I(Cl,swell) independent of pannexin-1 and that pannexin-1 hemichannels are not activated by swelling in HEK-293 cells.