Hypertonicity activated ion currents and ATP release in Xenopus laevis oocytes

BAZZI Z, BRACAMONTE MV, GUASTAFERRI FV, OZU M, SCHWARZBAUM P, GALIZIA L

Congreso; XLVII Reunión Anual SAB; 2018

The Xenopus laevis oocyte is a well-known heterologous expression system.Several endogenous ion channels and transporters of Xenopus oocytes have beenwell characterized, but the identification of volume-sensitive endogenous channelsis still a matter of debate. In native Xenopus oocytes hypertonic stimuli producesthe activation of an endogenous ion current and simultaneous ATP release.However, the effect of cell volume decrease on the activation of these endogenouschannels was not deeply investigated. Since ATP is mostly anionic at physiologicalpH, we wondered whether volume-sensitive ion channels mediating thisendogenous current would be responsible for the observed activation of ATP efflux.To approach this question, we used heterologous expression of aquaporins (AQPs)to produce rapid cell volume changes. In this work we evaluated cell volumechanges, the ionic currents and the ATP release induced by hypertonic stimuli inXenopus laevis oocytes with or without heterologous expression of humanaquaporin-1 (AQP1). Hypertonic-induced ion currents and ATP release weremeasured using two electrode voltage-clamp and luminometric techniques,respectively, while cell volume was monitored by videomicroscopy. In waterinjected oocytes (Ctrl) hypertonic stimuli induced cell volume decrease, activationof an endogenous ionic conductance (Ghyper) and a slow release of intracellularATP. In AQP1-expressing oocytes we observed a faster volume decrease, togetherwith a higher activation of Ghyper (Ghyper Ctrl = 4 ± 0.3 μS, n= 7 vs Ghyper AQP1 =90 ± 27 μS, n = 6, p<0.05) and higher activation of ATP release (Relative ATPhyperCtrl = 34 ± 7, n= 6 vs Relative ATPhyper AQP1 = 133 ± 23, n = 7, p <0.05). Resultssuggest the existence of an endogenous volume-sensitive ion channel at theXenopus laevis oocyte, mediating ATP release.