title: The non-steroidal anti-inflammatory drug, diclofenac, inhibits Na(+) current in rat myoblasts.
abstract: The inhibitory effect of diclofenac, a non-steroidal anti-inflammatory drug (NSAID), on the voltage-gated inward Na+ current (I(Na)) in cultured rat myoblasts was investigated using the whole-cell voltage-clamp technique. At concentrations of 10 nM-100 microM, diclofenac produced a dose-dependent and reversible inhibition of I(Na) with an IC50 of 8.51 microM, without modulating the fast activation and inactivation process. The inhibitory effect of diclofenac took place at resting channels and increased with more depolarizing holding potential. In addition to inhibiting the Na+ current amplitude, diclofenac significantly modulated the steady-state inactivation properties of the Na+ channels, but did not alter the steady-state activation. The steady-state inactivation curve was significantly shifted towards the hyperpolarizing potential in the presence of diclofenac. Furthermore, diclofenac treatment resulted in a fairly slow recovery from inactivation of the Na+ channel. The inhibitory effect of diclofenac was enhanced by repetitive pulses and was inflected by changing frequency; the blocking effect at higher frequency was significantly greater than at lower frequency. Both intracellular and extracellular application of diclofenac could inhibit I(Na), indicating that diclofenac may exert its channel inhibitory action both inside and outside the channel sites. Our data directly demonstrate that diclofenac can inhibit the inward Na+ channels in rat myoblasts. Some different inhibitory mechanisms from that in neuronal Na+ channels are discussed.
authors.affiliation: Center for Brain Science Research, Department of Physiology and Biophysics, School of Life Sciences, Fudan University, Shanghai 200433, China.
authors.forename: Xiao-Wei
authors.initials: XW
authors.lastname: Fei
authors.forename: Lin-Yun
authors.initials: LY
authors.lastname: Liu
authors.forename: Jian-Guang
authors.initials: JG
authors.lastname: Xu
authors.forename: Zhi-Hong
authors.initials: ZH
authors.lastname: Zhang
authors.forename: Yan-Ai
authors.initials: YA
authors.lastname: Mei
mesh_terms: D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D004008:Diclofenac / Q000494:pharmacology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D032446:Myoblasts / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000378:metabolism* / Q000502:physiology
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D015222:Sodium Channels; D004008:Diclofenac