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Characterization of a nicotinamide–adenine dinucleotide‐dependent cation channel in the CRI‐G1 rat insulinoma cell line
Author(s) -
Herson P. S.,
Dulock K. A.,
Ashford M. L. J.
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.065bc.x
Subject(s) - nad+ kinase , chemistry , biophysics , intracellular , conductance , membrane potential , nicotinamide adenine dinucleotide , gating , ion channel , nicotinamide , biochemistry , biology , enzyme , receptor , mathematics , combinatorics
1 Cell‐free excised membrane patches were used to examine the properties of a novel nicotinamide–adenine dinucleotide (β‐NAD + )‐activated ion channel in the rat insulin‐secreting cell line, CRI‐G1. 2 In inside‐out recordings, β‐NAD + (0.05–1.0 m m ) induced the appearance of a channel characterized by extremely slow kinetics, with mean open times in the range of seconds. The estimated EC 50 for activation was 114 μ m . Channel activity declined with time (run‐down) following activation by β‐NAD + in excised patches and this was not prevented by intra‐cellular application of trypsin. 3 The single channel current–voltage relationship was linear with a conductance of 74 pS in symmetrical NaCl. The channel appears equally permeable to Na + , K + and Cs + , exhibits an appreciable permeability to Ca 2+ , Mg 2+ and Ba 2+ , but excludes anions. 4 The channel displays an unusual voltage sensitivity, with an abrupt increase in open‐state probability at depolarized voltages. 5 Channel opening, in the presence of β‐NAD + , required both Ca 2+ and Mg 2+ to be present at the internal side of the membrane. Activation by Ca 2+ required a concentration of at least 10 μ m and was maximal at 0.1 m m . Ba 2+ did not substitute for Ca 2+ in inducing channel activity nor did it inhibit activation by Ca 2+ . Increasing the concentration of intracellular Mg 2+ stabilized the open state of NAD + ‐activated channels. 6 The non‐selective cation channel reported here differs in its gating and modulatory characteristics from non‐selective cation channels described in other tissues. This channel may play a role in the pathophysiological reponses of β‐cells to oxidative stress.