Functional and molecular identification of pH-sensitive K+ channels in murine urinary bladder smooth muscle.
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.


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 mM) and bupivacaine (100 microm) 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 mm), 4-aminopyridine (5 mM), glibenclamide (10 microm) or apamin (300 nM) did not inhibit the effects of low pH on outward current. However, treatment with lidocaine (1 mM) 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.


CONCLUSIONS
TASK channels are expressed in bladder smooth muscle and contribute to the basal K(+) conductances responsible for resting membrane potential.
Beckett
Elizabeth A H
EA
Department of Physiology and Cell Biology, University of Nevada Reno, School of Medicine, Reno, NV 89557, USA.
Han
Insoo
I
Baker
Salah A
SA
Han
Junguk
J
Britton
Fiona C
FC
Koh
Sang Don
SD
D000818:Animals; D015153:Blotting, Western; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009130:Muscle, Smooth / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D001743:Urinary Bladder / Q000502:physiology*
D024683:Potassium Channels, Tandem Pore Domain