title: Calcineurin-independent inhibition of KV1.3 by FK-506 (tacrolimus): a novel pharmacological property.
abstract: 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.
authors.affiliation: Department of Physiology, Collge of Medicine, Catholic University of Korea, 505 Banpo-dong, Socho-gu, Seoul 137-701, Korea.
authors.forename: Hye Sook
authors.initials: HS
authors.lastname: Ahn
authors.forename: Sung Eun
authors.initials: SE
authors.lastname: Kim
authors.forename: Bok Hee
authors.initials: BH
authors.lastname: Choi
authors.forename: Jin-Sung
authors.initials: JS
authors.lastname: Choi
authors.forename: Myung-Jun
authors.initials: MJ
authors.lastname: Kim
authors.forename: Duck-Joo
authors.initials: DJ
authors.lastname: Rhie
authors.forename: Shin Hee
authors.initials: SH
authors.lastname: Yoon
authors.forename: Yang-Hyeok
authors.initials: YH
authors.lastname: Jo
authors.forename: Myung-Suk
authors.initials: MS
authors.lastname: Kim
authors.forename: Ki-Wug
authors.initials: KW
authors.lastname: Sung
authors.forename: Oh-Joo
authors.initials: OJ
authors.lastname: Kwon
authors.forename: Sang June
authors.initials: SJ
authors.lastname: Hahn
mesh_terms: 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
chemical_list: 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