Expression and function of KV2-containing channels in human urinary bladder smooth muscle

Abstract

The functional role of the voltage-gated K+ (KV) channels in human detrusor smooth muscle (DSM) is largely unexplored. Here, we provide molecular, electrophysiological, and functional evidence for the expression of KV2.1, KV2.2, and the electrically silent KV9.3 subunits in human DSM. Stromatoxin-1 (ScTx1), a selective inhibitor of KV2.1, KV2.2, and KV4.2 homotetrameric channels and of KV2.1/9.3 heterotetrameric channels, was used to examine the role of these channels in human DSM function. Human DSM tissues were obtained during open bladder surgeries from patients without a history of overactive bladder. Freshly isolated human DSM cells were studied using RT-PCR, immunocytochemistry, live-cell Ca2+ imaging, and the perforated whole cell patch-clamp technique. Isometric DSM tension recordings of human DSM isolated strips were conducted using tissue baths. RT-PCR experiments showed mRNA expression of KV2.1, KV2.2, and KV9.3 (but not KV4.2) channel subunits in human isolated DSM cells. KV2.1 and KV2.2 protein expression was confirmed by Western blot analysis and immunocytochemistry. Perforated whole cell patch-clamp experiments revealed that ScTx1 (100 nM) inhibited the amplitude of the voltage step-induced KV current in freshly isolated human DSM cells. ScTx1 (100 nM) significantly increased the intracellular Ca2+ level in DSM cells. In human DSM isolated strips, ScTx1 (100 nM) increased the spontaneous phasic contraction amplitude and muscle force, and enhanced the amplitude of the electrical field stimulation-induced contractions within the range of 3.5–30 Hz stimulation frequencies. These findings reveal that ScTx1-sensitive KV2-containing channels are key regulators of human DSM excitability and contractility and may represent new targets for pharmacological or genetic intervention for bladder dysfunction.