Masaomi Tajimi

Changes in the Function and Expression of T-Type and N-Type Calcium Channels in the Rat Bladder after Bladder Outlet Obstruction

PURPOSEnWe evaluated possible changes in the function and expression of T-type and N-type Ca(2+) channels in the bladder of rats with bladder outlet obstruction.nnnMATERIALS AND METHODSnFemale Sprague Dawley® rats were divided into a group with bladder outlet obstruction created by partial urethral ligation and a sham operated group. Six weeks postoperatively we determined the mRNA expression of T-type and N-type Ca(2+) channels in the bladder, dorsal root ganglion and spinal cord. We also cystometrically investigated expression by intravenous administration of the T-Ca blocker RQ-00311610 or the N-type Ca(2+) channel blocker ω-conotoxin GVIA. We then performed in vitro functional studies of detrusor strips using these blockers.nnnRESULTSnmRNA expression of T-type Ca(2+) channels in the bladder detrusor and mucosa layers, and the spinal cord dorsal horn, and N-type Ca(2+) channels in the whole bladder and detrusor layer, and the spinal cord dorsal horn was greater in the obstructed group than the sham operated group. In obstructed rats bladder capacity and voided volume increased after RQ-00311610 administration but the number of nonvoiding contractions decreased after ω-conotoxin GVIA administration. Detrusor strips from obstructed rats showed weaker contractile responses to electrical field stimulation, particularly in regard to the purinergic component. ω-Conotoxin GVIA suppressed electrical field stimulation induced contractions only in the detrusor of obstructed rats, especially the cholinergic component.nnnCONCLUSIONSnBlocking T-type Ca(2+) channels increased bladder capacity while N-type Ca(2+) channel blockade inhibited nonvoiding contractions in rats with bladder outlet obstruction. Decreased bladder efferent neurotransmission occurred after bladder outlet obstruction, predominantly in its purinergic component and detrusor contractions via cholinergic neurotransmission were activated in a compensatory manner, probably via N-type Ca(2+) channel up-regulation.

Functional role of the transient receptor potential melastatin 8 (TRPM8) ion channel in the urinary bladder assessed by conscious cystometry and ex vivo measurements of single-unit mechanosensitive bladder afferent activities in the rat

To evaluate the role of the transient receptor potential melastatin 8 (TRPM8) channel on bladder mechanosensory function by using L‐menthol, a TRPM8 agonist, and RQ‐00203078 (RQ), a selective TRPM8 antagonist.

RQ-00201894: A motilin receptor agonist causing long-lasting facilitation of human gastric cholinergically-mediated contractions.

The aim was to characterise RQ-00201894, a novel non-macrolide motilin agonist, using human recombinant receptors and then investigate its ability to facilitate cholinergic activity in human stomach. A reporter gene assay assessed motilin receptor function. Selectivity of action was determined using a panel of different receptors, ion channels, transporters and enzymes. Cholinergically-mediated muscle contractions were evoked by electrical field stimulation (EFS) of human gastric antrum. The results showed that RQ-00201894, motilin and erythromycin acted as full motilin receptor agonists (EC50: 0.20, 0.11, 69xa0nM, respectively). In this function, RQ-00201894 had >90-fold selectivity of action over its ability to activate the human ghrelin receptor (EC50 19xa0nM) and greater selectivity over all other receptors/mechanisms tested. In human stomach RQ-00201894 0.1-30xa0μM concentration-dependently increased EFS-evoked contractions (up to 1209%; pEC50 6.0). At 0.1-10xa0μM this activity was usually prolonged. At higher concentrations (3-30xa0μM) RQ-00201894 also caused a short-lasting muscle contraction, temporally disconnected from the increase in EFS-evoked contractions. RQ-00201894 10xa0μM did not consistently affect submaximal contractions evoked by carbachol. In conclusion, RQ-00201894 potently and selectively activates the motilin receptor and causes long-lasting facilitation of cholinergic activity in human stomach, an activity thought to correlate with an ability to increase gastric emptying.