title: KV2.1 and electrically silent KV channel subunits control excitability and contractility of guinea pig detrusor smooth muscle.
abstract: Voltage-gated K(+) (K(V)) channels are implicated in detrusor smooth muscle (DSM) function. However, little is known about the functional role of the heterotetrameric K(V) channels in DSM. In this report, we provide molecular, electrophysiological, and functional evidence for the presence of K(V)2.1 and electrically silent K(V) channel subunits in guinea pig DSM. Stromatoxin-1 (ScTx1), a selective inhibitor of the homotetrameric K(V)2.1, K(V)2.2, and K(V)4.2 as well as the heterotetrameric K(V)2.1/6.3 and K(V)2.1/9.3 channels, was used to examine the role of these K(V) channels in DSM function. RT-PCR indicated mRNA expression of K(V)2.1, K(V)6.2-6.3, K(V)8.2, and K(V)9.1-9.3 subunits in isolated DSM cells. K(V)2.1 protein expression was confirmed by Western blot and immunocytochemistry. Perforated whole cell patch-clamp experiments revealed that ScTx1 (100 nM) inhibited the amplitude of the K(V) current in freshly isolated DSM cells. ScTx1 (100 nM) did not significantly change the steady-state activation and inactivation curves for K(V) current. However, ScTx1 (100 nM) decreased the activation time-constant of the K(V) current at positive voltages. Although our patch-clamp data could not exclude the presence of the homotetrameric K(V)2.1 channels, the biophysical characteristics of the ScTx1-sensitive current were consistent with the presence of heterotetrameric K(V)2.1/silent K(V) channels. Current-clamp recordings showed that ScTx1 (100 nM) did not change the DSM cell resting membrane potential. ScTx1 (100 nM) increased the spontaneous phasic contraction amplitude, muscle force, and muscle tone as well as the amplitude of the electrical field stimulation-induced contractions of isolated DSM strips. Collectively, our data revealed that K(V)2.1-containing channels are important physiological regulators of guinea pig DSM excitability and contractility.
authors: Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, USA.
authors: Kiril L
authors: KL
authors: Hristov
authors: Muyan
authors: M
authors: Chen
authors: Rupal P
authors: RP
authors: Soder
authors: Shankar P
authors: SP
authors: Parajuli
authors: Qiuping
authors: Q
authors: Cheng
authors: Whitney F
authors: WF
authors: Kellett
authors: Georgi V
authors: GV
authors: Petkov
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002316:Cardiotonic Agents / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051669:Shab Potassium Channels / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013111:Spider Venoms / Q000378:metabolism; D001743:Urinary Bladder / Q000033:anatomy & histology*
chemical_list: D002316:Cardiotonic Agents; D010455:Peptides; D021122:Protein Subunits; D051669:Shab Potassium Channels; D013111:Spider Venoms; C560803:stromatoxin protein, Stromatopelma calceata; D011189:Potassium Chloride; D002217:Carbachol