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[摘要]：Small conductance Ca(2+)-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 mu M) increased SK currents, which were blocked by apamin (1 mu M), a selective SK channel inhibitor. In current-clamp mode, SKA-31 (10 mu M) hyperpolarized the cell resting membrane potential, which was blocked by apamin (1 mu M) but not by 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) (1 mu M), a selective IK channel inhibitor. SKA-31 (10 nM-10 mu M) 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 mu M) but not by TRAM-34 (1 mu M), 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. |
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