title: Ca(2+)-blockable, poorly selective cation channels in the apical membrane of amphibian epithelia. UO2(2+) reveals two channel types.
abstract: This study deals with the effect of mucosal UO2(2+) on the Ca(2+)-blockable, poorly selective cation channels in the apical membrane of frog skin and toad urinary bladder. Our data show that UO2(2+) inhibits the Na+ currents through the amiloride-insensitive cation pathway and confirm a previously described stimulatory effect on the amiloride-blockade Na+ transport. Noise analysis of the Ca(2+)-blockable current demonstrates that the divalent also depresses the low-frequency Lorentzian (fc = 11.7 Hz) in the power density spectrum (PDS) and reveals the presence of high-frequency relaxation noise (fc = 58.5 Hz). The action of UO2(2+) is not reversed upon washout and is not accompanied by noise, typically induced by reversible blockers. The divalent merely depresses the plateau of the low-frequency Lorentzian, demonstrating a decrease in the number of conductive cation channels. Similarly, with mucosal K+ and Rb+, UO2(2+) also unmasks the high-frequency Lorentzian by depressing the noise from the slowly fluctuating cation channels (type S). In all experiments with mucosal Cs+, the PDS contains high-frequency relaxation noise (fc = 75.1 Hz in Rana temporaria, and 65.4 Hz in Rana ridibunda). An effect of UO2(2+) on the Cs+ currents and Lorentzian plateaus could not be demonstrated, suggesting that this monovalent cation does not pass through type S channels. Experiments with the urinary bladder revealed only a UO2(2+)-insensitive pathway permeable for Na+, K+, Rb+, and Cs+. We submit that in frog skin two cation-selective channels occur, distinguished by their spontaneous gating kinetics, their sensitivity to UO2(2+), and their permeability for Cs+. In toad urinary bladder, only one kind of cation-selective channel is observed, which resembles the UO2(2+)-insensitive channel in frog skin, with fast open-closed kinetics (type F).
authors.affiliation: Laboratory for Physiology, KULeuven, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Desmedt
authors.forename: J
authors.initials: J
authors.lastname: Simaels
authors.forename: W
authors.initials: W
authors.lastname: Van Driessche
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002024:Bufo marinus / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology*; D002586:Cesium / Q000378:metabolism; D004848:Epithelium / Q000502:physiology / Q000648:ultrastructure; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D009092:Mucous Membrane / Q000737:chemistry; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011895:Rana ridibunda / Q000502:physiology*; D011896:Rana temporaria / Q000502:physiology*; D012413:Rubidium / Q000378:metabolism; D012867:Skin / Q000648:ultrastructure; D012879:Skin Physiological Phenomena; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D014501:Uranium / Q000032:analysis / Q000494:pharmacology*; D001743:Urinary Bladder / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D007473:Ion Channels; D015221:Potassium Channels; D015222:Sodium Channels; D002586:Cesium; D014501:Uranium; D000584:Amiloride; D012413:Rubidium; D002118:Calcium