Purinergic control of AMPK activation by ATP released through connexin 43 hemichannels: pivotal roles in hemichannel-mediated cell injury

Abstract

Connexin hemichannels regulate many cell functions. However, the molecular mechanisms involved remain elusive. Given that hemichannel opening causes loss of ATP, we therefore speculated a potential implication of AMPK in the biological actions of hemichannels. Activation of hemichannels by removing extracellular Ca2+ led to an efflux of ATP and a weak activation of AMPK. Unexpectedly, dysfunction of hemichannels markedly potentiated AMPK activation, which was reproduced by promotion of extracellular ATP degradation or inhibition of P2 purinoceptors, but counteracted by exogenous ATP. Further analysis revealed that ATP induced a purinoceptor-dependent activation of Akt and mTOR. Suppression of Akt or mTOR augmented AMPK activation, whereas activation of Akt by transfection of cells with myr-Akt, a constitutively active form of Akt, abolished AMPK activation. In a pathological model of hemichannel opening triggered by cadmium, disclosure of hemichannels similarly enhanced AMPK activity, which protected cells from cadmium-induced cell injury through suppression of mTOR. Collectively, we unraveled a channel-mediated regulation of AMPK through purinergic signaling pathway. Furthermore, we defined AMPK as a pivotal molecule underlying the regulatory effects of hemichannels on cell survival.