Differential Effects of K<sup>+</sup> Channel Blockers on Phasic Contractility of Transverse and Longitudinal Rat Detrusor Strips

Abstract

Spontaneous phasic contractions of detrusor smooth muscle are pivotal to the normal bladder filling process. The role of K + channels in mediating phasic contractions has been investigated on different occasions, but only in detrusor strips isolated longitudinally. In this study, the effects of individual K + blockers were examined in both transverse and longitudinal detrusor strips. Detrusor strips were isolated transversely and longitudinally from young adult rat bladders. Tension before and after the introduction of K + channel blockers was measured using a myograph. Phasic activity was determined by calculating the integral of tension fluctuations. Phasic activity of transverse strips was increased under tetraethylammonium chloride (TEA), 4-aminopyridine (4-AP) and iberiotoxin (IbTx) treatments. Longitudinal phasic activity was increased under charybdotoxin (ChTx) treatment. Neither glibenclamide (Glib) nor apamin treatment elicited any significant effect in both transverse and longitudinal phasic activity. The results indicated that phasic activity was mediated differently depending on the contractile direction. Data from this study reiterate that in addition to the conventional longitudinal direction, the transverse direction also presents significance when examining the contractility of a sac-like organ like the bladder.