AJP - Renal Physiology, Vol 239, Issue 3 299-F306, Copyright © 1980 by American Physiological Society
Covalent modification and inhibition of an epithelial sodium channel by tyrosine-reactive reagents
C. S. Park and D. D. Fanestil
This study sought to elucidate the molecular mechanism involved in the Na+
entry across the apical membrane of the urinary bladder of the toad. Na+
transport, as measured by short-circuit current (SCC), was irreversibly
inhibited by three tyrosine-specific reagents: N-acetylimidazole (ID50, 4.6
x 10(-2)M), tetranitromethane (1.8 x 10(-4) M), and
7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl; 3.4 x 10(-5) M). The
functional specificity of NBD-Cl to block Na+ entry via Na+ channels was
attested by the following: 1) NBD-Cl produced comparable inhibition of SCC
and Na+ influx under aerobic and anaerobic conditions; 2) amphotericin B
produced complete recovery of inhibited SCC; 3) vasopressin increased SCC
only in proportion to the uninhibited SCC; 4) Km for Na+ was not changed;
and 5) the half time for the inhibition varied as a function of amiloride
concentration or pharmacologic activity of its analogues. On the basis of
the above findings, these tyrosine-specific reagents are believed to be
useful chemical probes for the identification and characterization of Na+
channel protein.
