title: Pharmacological activation of small conductance calcium-activated potassium channels with naphtho[1,2-d]thiazol-2-ylamine decreases guinea pig detrusor smooth muscle excitability and contractility.
abstract: Small conductance Ca²⁺-activated K⁺ (SK) and intermediate conductance Ca(2+)-activated K⁺ (IK) channels are thought to be involved in detrusor smooth muscle (DSM) excitability and contractility. Using naphtho[1,2-d]thiazol-2-ylamine (SKA-31), a novel and highly specific SK/IK channel activator, we investigated whether pharmacological activation of SK/IK channels reduced guinea pig DSM excitability and contractility. We detected the expression of all known isoforms of SK (SK1-SK3) and IK channels at mRNA and protein levels in DSM by single-cell reverse transcription-polymerase chain reaction and Western blot. Using the perforated patch-clamp technique on freshly isolated DSM cells, we observed that SKA-31 (10 μM) increased SK currents, which were blocked by apamin (1 μM), a selective SK channel inhibitor. In current-clamp mode, SKA-31 (10 μM) hyperpolarized the cell resting membrane potential, which was blocked by apamin (1 μM) but not by 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34) (1 μM), a selective IK channel inhibitor. SKA-31 (10 nM-10 μM) significantly inhibited the spontaneous phasic contraction amplitude, frequency, duration, and muscle force in DSM isolated strips. The SKA-31 inhibitory effects on DSM contractility were blocked by apamin (1 μM) but not by TRAM-34 (1 μM), which did not per se significantly affect DSM spontaneous contractility. SK channel activation with SKA-31 reduced contractions evoked by electrical field stimulation. SKA-31 effects were reversible upon washout. In conclusion, SK channels, but not IK channels, mediate SKA-31 effects in guinea pig DSM. Pharmacological activation of SK channels reduces DSM excitability and contractility and therefore may provide a novel therapeutic approach for controlling bladder dysfunction.
authors: Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208, USA.
authors: Shankar P
authors: SP
authors: Parajuli
authors: Rupal P
authors: RP
authors: Soder
authors: Kiril L
authors: KL
authors: Hristov
authors: Georgi V
authors: GV
authors: Petkov
mesh_terms: D000818:Animals; D052160:Benzothiazoles / Q000494:pharmacology*; D015153:Blotting, Western; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D002469:Cell Separation; D003627:Data Interpretation, Statistical; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000819:agonists*; D001743:Urinary Bladder / Q000187:drug effects* / Q000378:metabolism
chemical_list: D052160:Benzothiazoles; D002120:Calcium Channel Agonists; D012333:RNA, Messenger; D051640:Small-Conductance Calcium-Activated Potassium Channels; C535212:naphtho(1,2-d)thiazol-2-ylamine