Contractions and relaxations of the urinary bladder occur in all directions to facilitate urine release and storage. Transverse and longitudinal contractility of detrusor smooth muscle have been studied before using various pharmacologic stimuli but not β agonists. Given the importance of β-adrenoceptors in mediating bladder relaxation, the effects of isoprenaline (IPNA) in transverse and longitudinal contractility were examined. Pretreatment with a low concentration of IPNA (0.1 or 1 μM) suppressed carbachol (CCh)-induced contractions, more in the transverse than longitudinal direction. Increasing the IPNA concentration to 10 or 100 μM resulted in greater inhibition of longitudinal contractions. Also in the longitudinal direction, IPNA-induced relaxation was greater than in the transverse direction. When precontracted with a submaximal concentration of CCh (1 μM), IPNA increased the phasic activity in the longitudinal direction only. In summary, β-adrenoceptor-mediated differences between transverse and longitudinal contractility were revealed. In testing the relaxant properties of selective β-agonists, the findings here should be considered such that other than the conventional longitudinal contractions, measurements are also made in other directions.

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The data suggested heterogeneity in the regulation of directional detrusor contractility via NOS- and COX-associated mechanisms.

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.