Hypertonicity activated ion currents and ATP release in Xenopus laevis oocytes

BAZZI, ZAHER; OZU, MARCELO; BRACAMONTE, M. VICTORIA; SCHWARZBAUM, PABLO; GUASTAFERRI, FLORENCIA V.; GALIZIA, LUCIANO

La Plata, Pcia de Buenos Aires

Congreso; XL Reunión Anual de la Sociedad Argentina de Biofísica; 2018

Sociedad Argentina Biofísica

The Xenopus laevis oocyte is a well-known heterologous expression system. Several endogenous ion channels and transporters of Xenopus oocytes have been well characterized, but the identification of volume-sensitiveendogenous channelsis still a matter of debate. In native Xenopus oocytes hypertonic stimuli produces the activation of an endogenous ion current and simultaneous ATP release. However, the effect of cell volume decrease on the activation of these endogenous channels was not deeply investigated.Since ATP is mostly anionic at physiological pH, we wondered whether volume-sensitive ion channels mediating this endogenous 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 workwe evaluated cell volume changes, the ionic currents and the ATP release induced by hypertonic stimuli inXenopuslaevisoocytes with or without heterologous expression of human aquaporin-1 (AQP1).Hypertonic-induced ion currents and ATP release were measured using two electrode voltage-clamp and luminometric techniques, respectively, while cell volume was monitored by videomicroscopy. In water injected oocytes (Ctrl)hypertonic stimuli induced cell volume decrease, activation of an endogenous ionic conductance (Ghyper) and a slow release of intracellular ATP. In AQP1-expressing oocytes we observed a faster volume decrease, together with a higher activation of Ghyper(GhyperCtrl= 4 ± 0.3 µS, n= 7 vs GhyperAQP1 = 90 ± 27 µS, n = 6, p