Ion Currents Induced by ATP and Angiotensin II in Cultured Follicular Cells of Xenopus laevis

Abstract

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 wholecell 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 AT 1 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.

Purinergic signalling in the reproductive system in health and disease

“…Oocytes K + current responses to FSH or adenosine in monolayers of small follicular cells surrounding a single large oocyte of Xenopus are suppressed by ATP [136]. P2 receptors are expressed by the follicular cells of Xenopus [207,286]. Since UTP and ATP are equipotent, this effect could be mediated by a P2Y 2 or P2Y 4 receptor subtype [136].…”

Purinergic Signalling in the Reproductive System

“…Perifollicular and ovarian stromal cells express P1 and P2 receptors (King et al, 1996;Montiel-Herrera et al, 2011), and purinergic signalling in these cells can modulate oocytes development. In the Xenopusoocyte model, treatment with FSH and adenosine induced K + current responses in the follicular cells surrounding the oocyte, and cotreatment with ATP or UTP blocked the effect (Fujita et al, 2001).…”

Purinergic signaling pathways in endocrine system

“…Activation of P2Y 2 R and P2Y 6 R triggers mitogenic signaling pathways and cell proliferation in porcine ovarian theca cells (Vazquez-Cuevas et al, 2010). Follicular oocytes of Xenopus laevis express P2Y 2 R, which activation leads to generation of inward currents in a majority of cells (King et al, 1996; Montiel-Herrera et al, 2011), whereas adenosine stimulates hyperpolarizing potassium currents (Fujita et al, 2001). …”