EFFECTS OF LOCAL ANESTHETICS ON THE CONTRACTILITY OF RAT BLADDERS

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.

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 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.

CONCLUSION

TASK channels are expressed in bladder smooth muscle and contribute to the basal K(+) conductances responsible for resting membrane potential.

Management of post-operative bladder spasm

OBJECTIVE

Pain management following bladder surgery in children is often complicated by bladder spasm. The overall severity of spasm can be reduced with opioids, anticholinergic medication and sedatives, although breakthrough spasms often occur. At the Royal Children's Hospital, Melbourne, intravesical bupivacaine has been used to manage postoperative bladder spasm to good effect. The administration of intravesical bupivacaine is analysed in this prospective audit of locally applied intravesical anaesthetic and compared with other methods.

METHOD

From February to August 2003, histories of 58 patients who had intravesical bupivacaine were studied and compared with six other methods of management of postoperative bladder spasm.

CONCLUSION

Data showed that epidural anaesthesia was the most effective treatment of pain, with a pain score reduction of 6.6, compared with a reduction of 6.1 with intravesical bupivacaine, and 4.5 using intravenous morphine. However, intravesical bupivacaine was the most effective method for the relief of bladder spasm.