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CHARACTERIZATION OF A CATION CHANNEL ON THE APICAL SURFACE OF THE FROG LENS EPITHELIUM
Author(s) -
Jacob T. J. C.,
Bangham J. A.,
Duncan G.
Publication year - 1985
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1985.sp002925
Subject(s) - pipette , conductance , chemistry , time constant , amiloride , patch clamp , tetrodotoxin , analytical chemistry (journal) , biophysics , mathematics , chromatography , biology , biochemistry , sodium , combinatorics , receptor , organic chemistry , electrical engineering , engineering
The properties of a single conductance pathway of the apical (fibre‐facing) surface of the frog lens epithelium are reported. Using the patch‐clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981), the most common single‐channel currents had an amplitude of 1·9 pA, the mean open time 2·1 ms and a conductance of 25 pS. One open‐state time constant (t o = 3·3 ms) and two closed‐state time constants (τ c 1 = 0·9 ms, τ c 2 = 23·1 ms) were resolved. The channel current and the mean open time were both increased when Ca 2+ was removed from the external solution and the open time distribution was no longer fitted by a single exponential. Multiple‐channel events in cell‐attached patches containing two or more identical channels were distributed in a binomial fashion and the probability that an individual channel was open, obtained by fitting the binomial distribution, was 0·039. The channel was found to have a Na + :K + selectivity ratio of 3:1. When Ca 2+ was removed from the pipette solution the probability that an individual channel was open increased to 0·137 and the Na + :K + selectivity ratio increased to 4:1. Channel activity was observed in the presence of tetrodotoxin (10 −6 M) in the bathing medium and the pipette solution but was abolished by internal perfusion of the patch pipette with 0·5 x 10 −4 M amiloride. This apical conductance pathway is identified as an amiloride‐sensitive cation channel. These channels are clustered in groups on the apical membrane, spontaneously active at the resting potential and with the possibility of altering their Na + :K + selectivity. They represent a distinct type of channel, that differ from nerve and muscle Na + channels in their manner of activation, but do share some common features with both Na + and Ca 2+ channels in excitable cells.