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.
Highlights
Urine release and storage are major functions of the urinary bladder
In both transverse and longitudinal directions, phasic activity was significantly increased by 10 mM tetraethylammonium chloride (TEA) treatment (Figure 1(b))
Transverse phasic activity was increased by 110% ± 20%, compared to a 60% ± 10% increase in longitudinal phasic activity (P < 0.05)
Summary
Urine release and storage are major functions of the urinary bladder. Forceful contractions of the detrusor smooth muscle are essential for urine release. The ever changing contractility of the detrusor smooth muscle contributes to spontaneous phasic contractions frequently seen in whole bladder or isolated strip experiments. Findings from the normal rat bladder provide good references to identify diseased-induced changes in disease models. The vast majority of literature on bladder contractility of the rat (or other animals) reported on longitudinal contractions only, irrespective of contractile differences between transverse and longitudinal directions [11,12,13,14,15]. These differences point to the importance in considering contractions in more than one direction. This study is conducted to identify differential modulation by K+
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