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Functional and molecular identification of pH‐sensitive K + channels in murine urinary bladder smooth muscle
Author(s) -
Beckett Elizabeth A.H.,
Han Insoo,
Baker Salah A.,
Han Junguk,
Britton Fiona C.,
Koh Sang Don
Publication year - 2008
Publication title -
bju international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.773
H-Index - 148
eISSN - 1464-410X
pISSN - 1464-4096
DOI - 10.1111/j.1464-410x.2008.07541.x
Subject(s) - contractility , tetraethylammonium , myocyte , membrane potential , urinary bladder , patch clamp , apamin , medicine , isometric exercise , channel blocker , blot , voltage clamp , endocrinology , biophysics , microbiology and biotechnology , chemistry , potassium channel , electrophysiology , biochemistry , biology , calcium , potassium , organic chemistry , gene
OBJECTIVE To examine the role of pH‐sensitive K + channels in setting the resting membrane potential in murine bladder smooth muscle, as bladder contractility is influenced by the resting membrane potential, which is mainly regulated by background K + conductances. MATERIALS AND METHODS Using conventional microelectrode recordings, isometric tension measurements, patch‐clamp recordings, reverse transcription‐polymerase chain reaction (RT‐PCR), Western blotting and immunohistochemistry, we assessed bladder smooth muscle cells and tissues. RESULTS Acidic pH (pH 6.5) depolarized the resting membrane potential of murine bladder smooth muscles and increased muscle tone and contractility. The pH‐induced changes were not abolished by neuronal blockers or classical K + ‐channel antagonists. Lidocaine (1 m m ) and bupivacaine (100 µ m ) mimicked the effects of acidifying the external solution, and in the presence of lidocaine no further increase in contractility was induced by reducing the pH to 6.5. Voltage‐clamp experiments on freshly dispersed bladder myocytes showed that pH 6.5 decreased the outward current. Pre‐treatment of bladder myocytes with the classical K + antagonists tetraethylammonium (10 m m ), 4‐aminopyridine (5 m m ), glibenclamide (10 µ m ) or apamin (300 n m ) did not inhibit the effects of low pH on outward current. However, treatment with lidocaine (1 m m ) abolished the effects of acidic pH on outward current. RT‐PCR showed the expression of the acid‐sensitive K + channel (TASK)‐1 and TASK‐2 gene transcripts in murine bladder, and immunohistochemistry and Western blot analysis showed TASK‐1 and TASK‐2 channel expression and distribution in smooth muscle tissues and cells. CONCLUSION TASK channels are expressed in bladder smooth muscle and contribute to the basal K + conductances responsible for resting membrane potential.