Calcineurin-independent inhibition of KV1.3 by FK-506 (tacrolimus): a novel pharmacological property.
The interaction of FK-506 with K(V)1.3, stably expressed in Chinese hamster ovary cells, was investigated with the whole cell patch-clamp technique. FK-506 inhibited K(V)1.3 in a reversible, concentration-dependent manner with an IC(50) of 5.6 microM. Rapamycin, another immunosuppressant, produced effects that were similar to those of FK-506 (IC(50) = 6.7 microM). Other calcineurin inhibitors (cypermethrin or calcineurin autoinhibitory peptide) alone had no effect on the amplitude or kinetics of K(V)1.3. In addition, the inhibitory action of FK-506 continued, even after the inhibition of calcineurin activity. The inhibition produced by FK-506 was voltage dependent, increasing in the voltage range for channel activation. At potentials positive to 0 mV (where maximal conductance is reached), however, no voltage-dependent inhibition was found. FK-506 exhibited a strong use-dependent inhibition of K(V)1.3. FK-506 shifted the steady-state inactivation curves of K(V)1.3 in the hyperpolarizing direction in a concentration-dependent manner. The apparent dissociation constant for FK-506 to inhibit K(V)1.3 in the inactivated state was estimated from the concentration-dependent shift in the steady-state inactivation curve and was calculated to be 0.37 microM. Moreover, the rate of recovery from inactivation of K(V)1.3 was decreased. In inside-out patches, FK-506 not only reduced the current amplitude but also accelerated the rate of inactivation during depolarization. FK-506 also inhibited K(V)1.5 and K(V)4.3 in a concentration-dependent manner with IC(50) of 4.6 and 53.9 microM, respectively. The present results indicate that FK-506 inhibits K(V)1.3 directly and that this effect is not mediated via the inhibition of the phosphatase activity of calcineurin.
Ahn
Hye Sook
HS
Department of Physiology, Collge of Medicine, Catholic University of Korea, 505 Banpo-dong, Socho-gu, Seoul 137-701, Korea.
Kim
Sung Eun
SE
Choi
Bok Hee
BH
Choi
Jin-Sung
JS
Kim
Myung-Jun
MJ
Rhie
Duck-Joo
DJ
Yoon
Shin Hee
SH
Jo
Yang-Hyeok
YH
Kim
Myung-Suk
MS
Sung
Ki-Wug
KW
Kwon
Oh-Joo
OJ
Hahn
Sang June
SJ
D000818:Animals; D016466:CHO Cells; D019703:Calcineurin / Q000378:metabolism; D065095:Calcineurin Inhibitors; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007700:Kinetics; D051664:Kv1.3 Potassium Channel / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D051666:Kv1.5 Potassium Channel / Q000037:antagonists & inhibitors; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011722:Pyrethrins / Q000494:pharmacology; D051672:Shal Potassium Channels / Q000037:antagonists & inhibitors; D020123:Sirolimus / Q000494:pharmacology; D016559:Tacrolimus / Q000494:pharmacology*; D014162:Transfection
D065095:Calcineurin Inhibitors; D007166:Immunosuppressive Agents; D051664:Kv1.3 Potassium Channel; D051666:Kv1.5 Potassium Channel; D026902:Potassium Channel Blockers; D011722:Pyrethrins; D051672:Shal Potassium Channels; C017160:cypermethrin; D019703:Calcineurin; D020123:Sirolimus; D016559:Tacrolimus