N. Sato et al., BLOCK OF NA-PIG VENTRICULAR MYOCYTES( CHANNEL BY BEPRIDIL IN ISOLATEDGUINEA), European journal of pharmacology, 314(3), 1996, pp. 373-379
The effects of bepridil, a potent antiarrhythmic agent, on the Na+ cur
rent (I-Na) of single guinea-pig ventricular myocytes were studied usi
ng the whole-cell patch-clamp technique. Bepridil inhibited I-Na in a
dose-dependent manner without causing any change in the I-V relationsh
ip for I-Na. Bepridil suppressed I-Na with K-d values of 342 and 40 mu
M when cells were clamped to holding potentials of -140 and -90 mV, r
espectively. 10 mu M bepridil shifted the steady-state inactivation cu
rve for I-Na toward more negative potentials by 7.7 mV (n = 6). Beprid
il also produced marked use-dependent block with a rapid onset. Recove
ry of I-Na from inactivation was retarded (time constant 290 ms) at a
holding potential of -140 mV in the presence of 10 mu M bepridil. When
the onset of I-Na block was studied in experiments using a double-pul
se protocol, bepridil blocked I-Na by 11.5% after a 4-ms pre-pulse, bu
t significantly blocked it after pre-pulses longer than 16 ms. These r
esults suggest that: (1) bepridil has a higher affinity for the inacti
vated state than the resting state of Na+ channel; (2) the drug also p
roduces an open channel block; and (3) the drug shows a lidocaine-like
fast kinetic block of Na+ current.