2-Aminoethoxydiphenyl borate causes dissociation between membrane electrical and mechanical activity in guinea-pig urinary bladder smooth muscle

Abstract.

Physiological functions of urinary bladder profoundly reflect smooth muscle mechanical activity. Urinary bladder smooth muscle itself produces myogenic rhythmic contraction, and this spontaneous mechanical event could be the fundamental determinant of urinary bladder functions. The spontaneous contraction of urinary bladder smooth muscle is thought to be triggered primarily by the action potential generated in this smooth muscle cell. Modulators of ion channels contributing to the configuration of action potential also affect urinary bladder smooth muscle mechanical activity as expected exactly from the effects on the electrical event. In the present study, we show that the frequency of action potential recorded in intact strip of guinea-pig urinary bladder smooth muscle is dramatically increased by 2-aminoethoxydiphenyl borate (2-APB; 30 µM) from 0.2 Hz to 1 Hz (~500% increments). In contrast to an increasing effect expected from the membrane electrical alterations, mechanical activity (both contraction amplitude and frequency) of this smooth muscle is unexpectedly reduced by the same concentration of 2-APB to ~35% of the control. The present results firstly show an apparent dissociation of electrical-mechanical coupling in urinary bladder smooth muscle. The alteration of membrane electrical activity might not be the exclusive trigger mechanism responsible for the generation of spontaneous rhythmic contraction of this smooth muscle.