P2X7 is a purinergic receptor-channel; its activation by ATP elicits a broad set of cellular actions, from apoptosis to signals for survival. Here, P2X7 expression and function was studied in human ovarian carcinoma (OCA) cells, and biopsies from non-cancerous and cancer patients were analyzed by immunohistochemistry. Ovarian surface epithelium in healthy tissue expressed P2X7 at a high level that was maintained throughout the cancer. The cell lines SKOV-3 and CAOV-3 were used to investigate P2X7 functions in OCA. In SKOV-3 cells, selective stimulation of P2X7 by 2'(3')-O-(4-benzoylbenzoyl) adenosine-5'-triphosphate (BzATP) induced a dose-dependent increase of intracellular Ca(2+) concentration ([Ca(2+)](i)) but not cell death. Instead, BzATP increased the levels of phosphorylated ERK and AKT (pERK and pAKT), with an EC(50) of 44 ± 2 and 1.27 ± 0.5 μM, respectively; 10 μM BzATP evoked a maximum effect within 15 min that lasted for 120 min. Interestingly, basal levels of pERK and pAKT were decreased in the presence of apyrase in the medium, strongly suggesting an endogenous, ATP-mediated phenomenon. Accordingly: (i) mechanically stimulated cells generated a [Ca(2+)](i) increase that was abolished by apyrase; (ii) apyrase induced a decrease in culture viability, as measured by the MTS assay for mitochondrial activity; and (iii) incubation with 10 μM AZ10606120, a specific P2X7 antagonist and transfection with the dominant negative P2X7 mutant E496A, both reduced cell viability to 70.1 ± 8.9% and to 76.5 ± 5%, respectively, of control cultures. These observations suggested that P2X7 activity was auto-induced through ATP efflux; this increased pERK and pAKT levels that generated a positive feedback on cell viability.

Disorders in cell signaling mediated by ATP or histamine, activating specific membrane receptors, have been frequently associated with tumorigenesis. Among the elements of response to purinergic (and histaminergic) signaling, ion channel activation controls essential cellular processes in cancer, such as cell proliferation, motility, and death. Here, we studied the effects that ATP had on electrical properties of human ovarian adenocarcinoma cells named SKOV-3. ATP caused increase in intracellular Ca2+ concentration ([Ca2+]i) and, concurrently, it evoked a complex electrical response with a conspicuous outward component. This current was generated through P2Y2 receptor activation and opening of K+ channels, KCa3.1, as indicated by electrophysiological and pharmacological analysis, as well as by immunodetection and specific silencing of P2Y2 or KCa3.1 gene by esiRNA transfection. Low µM ATP concentration increased SKOV-3 cell migration, which was strongly inhibited by KCa3.1 channel blockers and by esiRNA-generated P2Y2 or KCa3.1 downregulation. Finally, in human ovarian tumors, the P2Y2 and KCa3.1 proteins are expressed and co-localized in neoplastic cells. Thus, stimulation of P2Y2 receptors expressed in SKOV-3 cells promotes motility through KCa3.1 activation. Since P2Y2 and KCa3.1 are co-expressed in primary tumors, our findings suggest that they may play a role in cancer progression.

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Inwardly rectifying K (Kir) channel expression signals at an advanced stage of maturation during oligodendroglial differentiation. Knocking down their expression halts the generation of myelin and produces severe abnormalities in the central nervous system. Kir4.1 is the main subunit involved in the tetrameric structure of Kir channels in glial cells; however, the precise composition of Kir channels expressed in oligodendrocytes (OLs) remains partially unknown, as participation of other subunits has been proposed. Kir channels are sensitive to H; thus, intracellular acidification produces Kir current inhibition. Since Kir subunits have differential sensitivity to H, we studied the effect of intracellular acidification on Kir currents expressed in cultured OLs derived from optic nerves of 12-day-old rats. Unexpectedly, Kir currents in OLs (2-4 DIV) did not change within the pH range of 8.0-5.0, as observed when using standard whole-cell voltage-clamp recording or when preserving cytoplasmic components with the perforated patch-clamp technique. In contrast, low pH inhibited astrocyte Kir currents, which was consistent with the involvement of the Kir4.1 subunit. The H-insensitivity expressed in OL Kir channels was not intrinsic because Kir cloning showed no difference in the sequence reported for the Kir4.1, Kir2.1, or Kir5.1 subunits. Moreover, when Kir channels were heterologously expressed in Xenopus oocytes they behaved as expected in their general properties and sensitivity to H. It is therefore concluded that Kir channel H-sensitivity in OLs is modulated through an extrinsic mechanism, probably by association with a modulatory component or by posttranslational modifications.

Xenopus follicles are endowed with specific receptors for ATP, ACh, and AII, transmitters proposed as follicular modulators of gamete growth and maturation in several species. Here, we studied ion-current responses elicited by stimulation of these receptors and their activation mechanisms using the voltage-clamp technique. All agonists elicited Cl(-) currents that depended on coupling between oocyte and follicular cells and on an increase in intracellular Ca(2+) concentration ([Ca(2+) ](i)), but they differed in their activation mechanisms and in the localization of the molecules involved. Both ATP and ACh generated fast Cl(-) (F(Cl)) currents, while AII activated an oscillatory response; a robust Ca(2+) influx linked specifically to F(Cl) activation elicited an inward current (I(iw,Ca)) which was carried mainly by Cl(-) ions, through channels with a sequence of permeability of SCN(-) > I(-) > Br(-) > Cl(-). Like F(Cl), I(iw,Ca) was not dependent on oocyte [Ca(2+) ](i) ; instead both were eliminated by preventing [Ca(2+) ](i) increase in the follicular cells, and also by U73122 and 2-APB, drugs that inhibit the phospolipase C (PLC) pathway. The results indicated that F(Cl) and I(iw,Ca) were produced by the expected, PLC-stimulated Ca(2+) -release and Ca(2+) -influx, respectively, and by the opening of I(Cl(Ca)) channels located in the follicular cells. Given their pharmacological characteristics and behavior in conditions of divalent cation deprivation, Ca(2+) -influx appeared to be driven through store-operated, calcium-like channels. The AII response, which is also known to require PLC activation, did not activate I(iw,Ca) and was strictly dependent on oocyte [Ca(2+) ](i) increase; thus, ATP and ACh receptors seem to be expressed in a population of follicular cells different from that expressing AII receptors, which were coupled to the oocyte through distinct gap-junction channels.