title: Myorelaxant action of fluorine-containing pinacidil analog, flocalin, in bladder smooth muscle is mediated by inhibition of L-type calcium channels rather than activation of KATP channels.
abstract: Flocalin (FLO) is a new ATP-sensitive K(+) (KATP) channel opener (KCO) derived from pinacidil (PIN) by adding fluorine group to the drug's structure. FLO acts as a potent cardioprotector against ischemia-reperfusion damage in isolated heart and whole animal models primarily via activating cardiac-specific Kir6.2/SUR2A KATP channels. Given that FLO also confers relaxation on several types of smooth muscles and can partially inhibit L-type Ca(2+) channels, in this study, we asked what is the mechanism of FLO action in bladder detrusor smooth muscle (DSM). The actions of FLO and PIN on contractility of rat and guinea pig DSM strips and membrane currents of isolated DSM cells were compared by tensiometry and patch clamp. Kir6 and SUR subunit expression in rat DSM was assayed by reverse transcription PCR (RT-PCR). In contrast to PIN (10 μM), FLO (10 μM) did not produce glibenclamide-sensitive DSM strips' relaxation and inhibition of spontaneous and electrically evoked contractions. However, FLO, but not PIN, inhibited contractions evoked by high K(+) depolarization. FLO (40 μM) did not change the level of isolated DSM cell's background K(+) current, but suppressed by 20 % L-type Ca(2+) current. Determining various Kir6 and SUR messenger RNA (mRNA) expressions in rat DSM by RT-PCR indicated that dominant KATP channel in rat DSM is of vascular type involving association of Kir6.1 and SUR2B subunits. Myorelaxant effects of FLO in bladder DSM are explained by partial blockade of L-type Ca(2+) channel-mediated Ca(2+) influx rather than by hyperpolarization associated with increased K(+) permeability. Thus, insertion of fluorine group in PIN's structure made the drug more discriminative between Kir6.2/SUR2A cardiac- and Kir6.1/SUR2B vascular-type KATP channels and rendered it partial L-type Ca(2+) channel-blocking potency.
authors.affiliation: Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine.
authors.forename: Igor B
authors.initials: IB
authors.lastname: Philyppov
authors.affiliation: Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine.
authors.forename: Andriy А
authors.initials: AА
authors.lastname: Golub
authors.affiliation: International Center of Molecular Physiology, National Academy of Sciences of Ukraine, Bogomoletz Str., 4, Kyiv, 01024, Ukraine.
authors.forename: Oleksiy I
authors.initials: OI
authors.lastname: Boldyriev
authors.affiliation: Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine.
authors.forename: Natalia L
authors.initials: NL
authors.lastname: Shtefan
authors.affiliation: International Center of Molecular Physiology, National Academy of Sciences of Ukraine, Bogomoletz Str., 4, Kyiv, 01024, Ukraine.
authors.forename: Khrystyna
authors.initials: K
authors.lastname: Totska
authors.affiliation: International Center of Molecular Physiology, National Academy of Sciences of Ukraine, Bogomoletz Str., 4, Kyiv, 01024, Ukraine.
authors.forename: Oleg I
authors.initials: OI
authors.lastname: Voitychuk
authors.affiliation: Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine. yshuba@biph.kiev.ua.|International Center of Molecular Physiology, National Academy of Sciences of Ukraine, Bogomoletz Str., 4, Kyiv, 01024, Ukraine. yshuba@biph.kiev.ua.
authors.forename: Yaroslav M
authors.initials: YM
authors.lastname: Shuba
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000378:metabolism; D004558:Electric Stimulation; D006168:Guinea Pigs; D066298:In Vitro Techniques; D054086:KATP Channels / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D015394:Molecular Structure; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D020110:Pinacidil / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D064233:Sulfonylurea Receptors / Q000819:agonists / Q000378:metabolism; D001743:Urinary Bladder / Q000187:drug effects* / Q000378:metabolism
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D054086:KATP Channels; C559719:N-(4-difluoromethoxyphenyl)-N'-pinacolyl-N''-cyanoguanidine; D064233:Sulfonylurea Receptors; C092520:uK-ATP-1 potassium channel; D020110:Pinacidil
keywords: Bladder; Contraction; Detrusor smooth muscle; Flocalin; Guinea pig; KATP channels; L-type Ca2+ channels; Patch clamp; Pinacidil; Rat