Blockade of Voltage-Sensitive K+ Channels Increases Contractility More in Transverse Than in Longitudinal Rat Detrusor Strips

Objectives To investigate the effects of voltage-sensitive K+ channel blockade on phasic contractions in transverse (TR) and longitudinal (LO) rat detrusor strips. The contractility of LO detrusor strips has been studied more extensively than that of TR ones, with the latter hardly used in experiments. Phasic contractions, regulated by various types of K+ channels, are present in normal bladders and are more commonly seen in diseased bladders. Methods Contractility was measured in TR and LO detrusor strips from young adult rats. Concentration–response curves of tetraethylammonium and 4-aminopyridine (4-AP) were constructed. Both the mean developed tension and the cyclic height of the phasic contractions were determined. Results At ≥10−2 mol/L, tetraethylammonium increased the developed tension and amplitude of the phasic contractions without differences between the TR and LO strips. 4-AP also increased the developed tension and amplitude of the phasic contractions but with greater effects in the TR than in the LO strips. At a maximal 4-AP concentration (10−2 mol/L), the mean developed tension was 52.96% ± 6.39% in the TR strips and 28.88% ± 5.91% in the LO strips. The amplitude of the phasic contractions was 11.07% ± 2.78% for the TR strips and 3.15% ± 1.31% for the LO strips. Conclusions Both nonselective K+ channel blockade by tetraethylammonium and selective voltage-sensitive K+ channel blockade by 4-AP resulted in increased contractions in LO and TR strips; however, the latter displayed greater effects only with 4-AP treatment. Thus, measuring detrusor contractions in different orientations might reveal heterogeneous responses that are dependent on the pharmacologic stimulus.