C. Toma et al., ACTIVATION OF POTASSIUM CURRENTS BY INHIBITORS OF CALCIUM-ACTIVATED CHLORIDE CONDUCTANCE IN RABBIT PORTAL-VEIN SMOOTH-MUSCLE CELLS, British Journal of Pharmacology, 118(3), 1996, pp. 513-520
1 The conventional whole-cell recording technique was used to study th
e effects of the chloride channel inhibitors ethacrynic acid, anthrace
ne-9-carboxylic acid (A-9-C) and indanyloxyacetic acid (IAA) on membra
ne currents in rabbit portal vein smooth muscle cells at a holding pot
ential of 0 mV. 2 Using a pipette solution that contained 1 x 10(-4) M
1,2-bis (2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) an
d a normal bathing solution the addition of ethacrynic acid (2 x 10(-4
) M to 1 x 10(-3) M) inhibited spontaneous transient outward currents
(STOCs) and evoked a concentration-dependent current at a holding pote
ntial of 0 mV. A similar current was activated by IAA (5 x 10(-4) M to
1 x 10(-3) M) but not by A-9-C (1-5 x 10(-3) M) at a holding potentia
l of 0 mV. 3 The amplitude of the current evoked by ethacrynic acid an
d IAA was linearly related to potential between -30 and 0 mV and displ
ayed outward rectification at positive potentials. The current induced
by A-9-C was evident only at potentials positive to +20 mV. 4 Glibenc
lamide (1 x 10(-5) M) abolished the current evoked by ethacrynic acid
and IAA at potentials negative to +10 mV and partially inhibited the c
urrent positive to +10 mV. The glibenclamide-insensitive current at po
sitive potentials was completely inhibited by 1 x 10(-3) M TEA. The A-
g-C-evoked current was insensitive to glibenclamide and abolished by 1
x 10(-3) M TEA. 5 The glibenclamide-sensitive current activated by et
hacrynic acid was not sustained and declined to control levels in the
continued presence of ethacrynic acid. However, the outwardly rectifyi
ng current recorded at +50 mV was well maintained over the same period
. 6 Outwardly rectifying currents evoked by ethacrynic acid and A-9-C
were observed with a pipette solution containing 1 x 10(-2) M BAPTA in
cells bathed in Ca-free extracellular solution containing 5 x 10(-4)
M BAPTA and 1 x 10(-5) M cyclopiazonic acid. 7 It is concluded that al
l three chloride-channel blockers activated an outwardly rectifying, T
EA-sensitive current. Moreover, ethacrynic acid and IAA evoked an addi
tional glibenclamide-sensitive current which was present at all potent
ials between -30 and +50 mV.