Mechanism of block by fluoxetine of 5-hydroxytryptamine3 (5-HT3)-mediated currents in NCB-20 neuroblastoma cells.
The effect of fluoxetine (Prozac) on 5-hydroxytryptamine(3) (5-HT(3))-mediated currents in NCB-20 neuroblastoma cells was examined using the whole-cell patch-clamp technique. Fluoxetine produced a significant reduction of peak amplitude without altering the activation time course of 5-HT(3)-mediated currents. These effects were concentration-dependent, with an IC(50) value of 4.15 microM. No voltage dependence was evident in fluoxetine's block of 5-HT(3)-mediated currents over the entire voltage range tested. The extent of block by pre-application of fluoxetine was significantly greater than that by co-application. Fluoxetine also increased the apparent rate of current desensitization to 5-HT application. Using a first-order kinetics analysis, the open-channel blocking rate constants were 0.06 microM(-1)s(-1) (k(+1), association rate constant) and 0.05 s(-1) (k(-1), dissociation rate constant), with an apparent K(d) (=k(-1)/k(+1)) of 0.83 microM. This value is close to an IC(50) of 1.11 microM obtained from the reduction in tau, the time constant of desensitization. Intracellular application of fluoxetine for long durations had no effect on the amplitude or kinetics of 5-HT(3)-mediated currents. Similarly, norfluoxetine, the major metabolite of fluoxetine, reduced the peak current, and enhanced the rate of current desensitization in a concentration-dependent manner with an IC(50) of 2.66 microM, indicating that norfluoxetine is more potent than fluoxetine in blocking 5-HT(3)-mediated currents. These results indicate that, at clinically relevant concentrations, fluoxetine and its metabolite, norfluoxetine, block 5-HT(3)-mediated currents in NCB-20 neuroblastoma cells.
Choi
Jin-Sung
JS
Department of Physiology, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Socho-gu, Seoul 137-701, South Korea.
Choi
Bok Hee
BH
Ahn
Hye Sook
HS
Kim
Myung-Jun
MJ
Rhie
Duck-Joo
DJ
Yoon
Shin Hee
SH
Min
Do Sik
DS
Jo
Yang-Hyeok
YH
Kim
Myung-Suk
MS
Sung
Ki-Wug
KW
Hahn
Sang June
SJ
D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D005473:Fluoxetine / Q000494:pharmacology*; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009447:Neuroblastoma / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D044406:Receptors, Serotonin, 5-HT3 / Q000502:physiology; D058831:Serotonin 5-HT3 Receptor Antagonists; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*
D005473:Fluoxetine; D044406:Receptors, Serotonin, 5-HT3; D058831:Serotonin 5-HT3 Receptor Antagonists; D017367:Selective Serotonin Reuptake Inhibitors