Hydrostatic pressure activates ATP-sensitive K channels in lung epithelium by ATP release through pannexin and connexin hemichannels

Abstract

Lungs of air-breathing vertebrates are constantly exposed to mechanical forces and therefore are suitable for investigation of mechanotransduction processes in nonexcitable cells and tissues. Freshly dissected Xenopus laevis lungs were used for transepithelial shortcircuit current (ISC) recordings and were exposed to increased hydrostatic pressure (HP; 5 cm fluid column, modified Ussing chamber). ISC values obtained under HP (I5cm) were normalized to values before HP (I0cm) application (I 5cm/I0cm). Under control conditions, HP decreased I SC (I5cm/I0cm=0.84; n=68; P<0.0001). This effect was reversible and repeatable >30 times. Preincubation with ATP-sensitive K+ channel (KATP) inhibitors (HMR1098 and glibenclamide) prevented the decrease in ISC (I5cm/I 0cm: HMR1098=1.19, P<0.0001; glibenclamide=1.11, P<0.0001). Similar effects were observed with hemichannel inhibitors (I5cm/ I0cm: meclofenamic acid=1.09, P<0.0001; probenecid=1.0, P<0.0001). The HP effect was accompanied by release of ATP (P<0.05), determined by luciferin-luciferase luminescence in perfusion solution from the luminal side of an Ussing chamber. ATP release was abrogated by both meclofenamic acid and probenecid. RT-PCR experiments revealed the expression of pannexin and connexin hemichannels and KATP subunit transcripts in X. laevis lung. These data show an activation of KATP in pulmonary epithelial cells in response to HP that is induced by ATP release through mechanosensitive pannexin and connexin hemichannels. These findings represent a novel mechanism of mechanotransduction in nonexcitable cells.