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 short-circuit current (ISC) recordings and were exposed to increased hydrostatic pressure (HP; 5 cm fluid column, modified Ussing chamber). I(SC) values obtained under HP (I(5cm)) were normalized to values before HP (I(0cm)) application (I(5cm)/I(0cm)). Under control conditions, HP decreased I(SC) (I(5cm)/I(0cm)=0.84; n=68; P<0.0001). This effect was reversible and repeatable ≥30 times. Preincubation with ATP-sensitive K(+) channel (K(ATP)) inhibitors (HMR1098 and glibenclamide) prevented the decrease in I(SC) (I(5cm)/I(0cm): HMR1098=1.19, P<0.0001; glibenclamide=1.11, P<0.0001). Similar effects were observed with hemichannel inhibitors (I(5cm)/I(0cm): 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.

Integrin-mediated transactivation of P2X7R via hemichannel-dependent ATP release stimulates astrocyte migration

“…Several authors have described ATP release via connexins or pannexins, but evidence suggesting a requirement for both hemichannels in response to a single ligand is limited. ATP release through connexin and pannexin hemichannels has been reported in lung epithelium cells [62]. Additionally, in spinal cord or cerebral astrocytes, ATP release via both hemichannels reportedly also activates P2X7R in response to fibroblast growth factor (FGF) or ultrafine carbon black [32,63].…”

Powerful partnership: crosstalk between pannexin 1 and the cytoskeleton

“…Recently, Richter and colleagues confirmed the role of Panx1 in ATP release from lung epithelial cells in response to stretch. In this case ATP release via Panx1 was elicited by changes in hydrostatic pressure (Richter et al, 2014). An intriguing downstream effect of the hydrostatic pressure-induced ATP release from cells was a concomitant activation of K ATP channels.…”

“…These expression system findings have since been expanded to erythrocytes (Locovei et al, 2006), lung epithelium (Seminario-Vidal et al, 2011; Richter et al, 2014), and more recently, neurons (Xia et al, 2012). Further, Panx1 has been shown to physically interact with the actin cytoskeleton (Bhalla-Gehi et al, 2010; Wicki-Stordeur and Swayne, 2013) and the expression of Panx1 exhibits a significant level of control over multiple cytoskeletal elements (Penuela et al, 2012).…”

Calcium-induced calcium release and gap junctions mediate large-scale calcium waves in olfactory ensheathing cells in situ

“…8). We cannot entirely exclude the involvement of connexin hemichannnels, since the gap junction blockers used in the present study, carbenoxolone and meclofenamic acid, have also been shown to block hemichannels [47]. ATP release through connnexin hemichannels is involved in Ca 2+ wave propagation in astrocytes [3], however, lack of ATP sensitivity of OECs renders the contribution of this mechanism to Ca 2+ waves in OECs unlikely.…”