title: Cu2+ reveals amiloride-induced activation and blocking of non-selective cation channel in larval bullfrog skin.
abstract: The non-selective cation channel (NSCC) in the larval bullfrog skin contributes to the short-circuit current (SCC) across the skin. The effects of amiloride and acetylcholine on the SCC were examined in the presence or absence of Cu2+ to determine whether the amiloride binding site mediating activation or that mediating inhibition of the channel is blocked by Cu2+ and whether amiloride and acetylcholine share a common binding site on the NSCC. The skin of tadpoles raised in aldosterone was examined with K-Ringer present on the apical side to potentiate the SCC. Amiloride (10(-4) M) transiently increased SCC in the absence of Cu2+. Apical application of 500 microM Cu2+ increased the SCC. In the presence of Cu2+, amiloride decreased the SCC. In contrast, acetylcholine (1 mM) transiently increased SCC whether Cu2+ was present or not. These results suggest that there are two binding sites for amiloride on the NSCC, whereby the site that activates the channel is blocked by Cu2+ while the site that inhibits it is not, and that the binding sites for acetylcholine and amiloride may be different.
authors.affiliation: Department of Physiology, Saitama Medical School, Moroyama, Iruma-gunn, Japan. makokam@saitama-med.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Takada
authors.forename: M
authors.initials: M
authors.lastname: Kasai
authors.forename: M
authors.initials: M
authors.lastname: Shibashi
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D003300:Copper / Q000494:pharmacology*; D004232:Diuretics / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism*; D007814:Larva; D008564:Membrane Potentials / Q000187:drug effects; D011892:Rana catesbeiana; D012867:Skin / Q000378:metabolism*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D004232:Diuretics; D007473:Ion Channels; D014665:Vasodilator Agents; D003300:Copper; D000584:Amiloride; D000109:Acetylcholine