Swelling-activated and arachidonic acid-induced currents are TREK-1 in rat bladder smooth muscle cells

Using the perforated patch voltage clamp, we investigated swelling-activated ionic channels (SACs) in rat urinary bladder smooth muscle cells.　Hypo-osmotic (60%) bath solution increased a membrane current which was inhibited by the SAC inhibitor, gadolinium.　The reversal potential of the hypotonicity-induced current shifted in the positive direction by increasing external K(+) concentration.　The hypotonicity-induced current was inhibited by extracellular acidic pH, phorbol ester and forskolin.　These pharmacological properties are identical to those of arachidonic acid-induced current present in these cells, suggesting the presence of TREK-1, a four-transmembrane two pore domain K(+) channel.　Using RT-PCR we screened rat bladder smooth muscles and cerebellum for expression of TREK-1, TREK-2 and TRAAK mRNAs.　Only TREK-1 mRNA was expressed in the bladder, while all three were expressed in the cerebellum.　We conclude that a mechanosensitive K(+) channel is present in rat bladder myocytes, which is activated by arachidonic acid and most likely is TREK-1.　This K(+) channel may have an important role in the regulation of bladder smooth muscle tone during urine storage.