title: Cloning and characterization of a functional P2X receptor from larval bullfrog skin.
abstract: ATP activates an apical-to-basolateral nonselective cation current across the skin of larval bullfrogs (Rana catesbeiana) with similarities to currents carried by some P2X receptors. A functional P2X receptor was cloned from tadpole skin RNA that encodes a 409-amino acid protein with highest protein homology to cP2X(8). RT-PCR showed that this transcript was found in skin, heart, eye, brain, and skeletal muscle of tadpoles but not in skin, brain, or heart of adults. After transcribed RNA from this clone was injected into Xenopus oocytes, application of ATP activated a transient current similar to other P2X receptors and the ATP-activated transient in short-circuit current (I(sc)) across intact skin. The agonists 2-methylthio-ATP and adenosine-5'-O-(thiotriphoshate) also activated transient currents. alpha,beta-Methylene-ATP and ADP were poor agonists of this receptor. Suramin and pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid tetrasodium (PPADS) were potent antagonists, and PPADS showed an irreversible blockade of this receptor to agonist activation. Under external Na(+)-free, Ca(2+)/Mg(2+)-free conditions (N-methyl-D-glucamine replacement, 0.5 mM EGTA), ATP activated a steadily increasing inward current. Fluorescence microscopy showed that propidium was entering the cells, suggesting that a relatively large pore size was formed under zero divalent conditions. This clone has some characteristics consistent with previously described ATP-activated I(sc) in the tadpole skin. Because the clone is not found in adult skin, it may have some exclusive role in the tadpole such as sensory reception by the skin or triggering apoptosis at metamorphosis.
authors.affiliation: Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois 62901, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Jensik
authors.forename: D
authors.initials: D
authors.lastname: Holbird
authors.forename: M W
authors.initials: MW
authors.lastname: Collard
authors.forename: T C
authors.initials: TC
authors.lastname: Cox
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000494:pharmacology; D003001:Cloning, Molecular; D017931:DNA Primers; D005260:Female; D066298:In Vitro Techniques; D007814:Larva; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D016133:Polymerase Chain Reaction; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D011892:Rana catesbeiana; D018048:Receptors, Purinergic P2 / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D058485:Receptors, Purinergic P2X5; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012879:Skin Physiological Phenomena; D014982:Xenopus laevis
chemical_list: D017931:DNA Primers; D018048:Receptors, Purinergic P2; D058485:Receptors, Purinergic P2X5; D011994:Recombinant Proteins; C408879:purinergic P2X8 receptor; D012313:RNA; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium