Novel mechanism of hydrogen sulfide-induced guinea pig urinary bladder smooth muscle contraction: role of BK channels and cholinergic neurotransmission.

Hydrogen sulfide (H2S) is a key signaling molecule regulating important physiological processes, including smooth muscle function. However, the mechanisms underlying H2S-induced detrusor smooth muscle (DSM) contractions are not well understood. This study investigates the cellular and tissue mechanisms by which H2S regulates DSM contractility, excitatory neurotransmission, and large-conductance voltage- and Ca(2+)-activated K(+) (BK) channels in freshly isolated guinea pig DSM. We used a multidisciplinary experimental approach including isometric DSM tension recordings, colorimetric ACh measurement, Ca(2+) imaging, and patch-clamp electrophysiology. In isolated DSM strips, the novel slow release H2S donor, P-(4-methoxyphenyl)-p-4-morpholinylphosphinodithioic acid morpholine salt (GYY4137), significantly increased the spontaneous phasic and nerve-evoked DSM contractions. The blockade of neuronal voltage-gated Na(+) channels or muscarinic ACh receptors with tetrodotoxin or atropine, respectively, reduced the stimulatory effect of GYY4137 on DSM contractility. GYY4137 increased ACh release from bladder nerves, which was inhibited upon blockade of L-type voltage-gated Ca(2+) channels with nifedipine. Furthermore, GYY4137 increased the amplitude of the Ca(2+) transients and basal Ca(2+) levels in isolated DSM strips. GYY4137 reduced the DSM relaxation induced by the BK channel opener, NS11021. In freshly isolated DSM cells, GYY4137 decreased the amplitude and frequency of transient BK currents recorded in a perforated whole cell configuration and reduced the single BK channel open probability measured in excised inside-out patches. GYY4137 inhibited spontaneous transient hyperpolarizations and depolarized the DSM cell membrane potential. Our results reveal the novel findings that H2S increases spontaneous phasic and nerve-evoked DSM contractions by activating ACh release from bladder nerves in combination with a direct inhibition of DSM BK channels.