Ion Currents Induced by ATP and Angiotensin Ⅱ in Cultured Follicular Cells of Xenopus laevis
2011
Montiel-Herrera, Marcelino, Universidad Nacional Autonoma de Mexico, Campus Juriquilla, Juriquilla, Queretaro, Mexico | Zaske, Ana Maria, Universidad Nacional Autonoma de Mexico, Campus Juriquilla, Juriquilla, Queretaro, Mexico | Garcia-Colunga, Jesus, Universidad Nacional Autonoma de Mexico, Campus Juriquilla, Juriquilla, Queretaro, Mexico | Martinez-Torres, Ataulfo, Universidad Nacional Autonoma de Mexico, Campus Juriquilla, Juriquilla, Queretaro, Mexico | Miledi, Ricardo, Universidad Nacional Autonoma de Mexico, Campus Juriquilla, Juriquilla, Queretaro, Mexico
Xenopus laevis oocytes are commonly used to study the biophysical and pharmacological properties of foreign ion channels and receptors, but little is known about those endogenously expressed in their enveloping layer of follicular cells (FCs). Whole-cell recordings and the perforated patch-clamp technique in cultured FCs held at -60 mV revealed that ATP (20-250 μM) generates inward currents of 465 ± 93 pA (mean ± standard error) in ∼60% of the FCs studied, whereas outward currents of 317 ± 100 pA were found in ∼5% of the cells. The net effect of ATP on the FCs was to activate both mono- and biphasic inward currents, with an associated increase in membrane chloride conductance. Two-microelectrode voltage-clamp recordings of nude oocytes held at -60 mV disclosed that ATP elicited biphasic inward currents, corresponding to the well-known F∧in and S∧in-like currents. ATP receptor antagonists like suramin, TNP-ATP, and RB2 did not inhibit any of these responses. On the other hand, when using whole-cell recordings, 1 μM Ang Ⅱ yielded smooth inward currents of 157 ± 45 pA in ∼16% of the FC held at -60 mV. The net Ang Ⅱ response, mediated by the activation of the AT₁ receptor, was a chloride current inhibited by 10 nM ZD7155. This study will help to better understand the roles of ATP and Ang Ⅱ receptors in the physiology of X. laevis oocytes.
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