title: Frog atrial natriuretic peptide and cGMP activate amiloride-sensitive Na(+) channels in urinary bladder cells of Japanese tree frog, Hyla japonica.
abstract: In our previous study, it was suggested that ANP and cGMP may increase Na(+) absorption in the urinary bladder of the Japanese tree frog, Hyla japonica. Thus, Na(+) transport activated by ANP was investigated electrophysiologically by using a cell-attached patch-clamp technique in freshly isolated cells from the urinary bladder. A predominant channel expressed was a low conductance Na(+) channel in the epithelial cells. The channel exhibited conductance for inward currents of 4.9 +/- 0.2 pS, long open and closed times (c.a. 190 ms), and positive reversal potential. The channel activity was decreased under the pipette solution including 10(-6) M amiloride. These characteristics were similar to those of amiloride-sensitive Na(+) channels (ENaC). Addition of 10(-9) M ANP activated and significantly increased the ENaC activity from 0.58 +/- 0.09 to 1.47 +/- 0.34. On the other hand, mean amplitudes and conductance of single channel did not change significantly after the addition of ANP. Addition of 10(-5) M 8-Br-cGMP also activated the ENaC and significantly increased the channel activity from 0.56 +/- 0.10 to 2.00 +/- 0.33. The addition of ANP failed to activate the ENaC in the presence of 10(-6) M amiloride. These results suggested that ANP and cGMP activate Na(+) transport via ENaC in the epithelial cells of frog urinary bladder.
authors.affiliation: Department of Life and Environmental Science, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
authors.forename: Toshiki
authors.initials: T
authors.lastname: Yamada
authors.forename: Norifumi
authors.initials: N
authors.lastname: Konno
authors.forename: Kouhei
authors.initials: K
authors.lastname: Matsuda
authors.forename: Minoru
authors.initials: M
authors.lastname: Uchiyama
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001001:Anura / Q000502:physiology*; D009320:Atrial Natriuretic Factor / Q000494:pharmacology / Q000502:physiology*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D004553:Electric Conductivity; D053503:Epithelial Sodium Channels / Q000187:drug effects / Q000502:physiology*; D005260:Female; D008297:Male; D018408:Patch-Clamp Techniques; D026941:Sodium Channel Blockers / Q000494:pharmacology; D001743:Urinary Bladder / Q000166:cytology / Q000378:metabolism*
chemical_list: D053503:Epithelial Sodium Channels; D026941:Sodium Channel Blockers; C016276:8-bromocyclic GMP; D000584:Amiloride; D009320:Atrial Natriuretic Factor; D006152:Cyclic GMP