郭育成、張宏江¹、謝汝敦¹

                              台北市立聯合醫院泌尿科；¹國立台灣大學醫學系泌尿科       

Yuh-Chen Kuo, Hong-Chiang Chang¹, Ju-Ton Hsieh¹

Department of Urology, Taipei City Hospital, Taipei, Taiwan; Department of Urology¹, School of Medicine, National Taiwan University, Taipei, Taiwan

 

Purpose: Previous study has demonstrated chloride transport inhibitors and chloride channel (CC) blockers could significantly suppress the norepinephine induced tonic contractility in rat bladder smooth muscle (SM) tissue. We investigated the dose-response effects of chloride transport inhibitors and CC blockers on the phasic and carbachol (CCh)-induced tonic contractions of bladder SM in rats with cyclophosphamide (CYP)-induced overactive bladder (OAB).

Materials and Methods: Three groups (CYPc40, CYPc80 and control) of twelve adult male Sprague Dawley rats (10–12 weeks) were used. CYP-induced OAB was provoked by four i.p injections in 7 days (CYPc40: 40 mg/kg and CYPc80: 80 mg/kg). Control rat received saline injections. The injections were done on days 0, 2, 4, and 6. The bladder tissues were harvested on day 7. We conducted a strategy involving organ bath isometric tension experiments involving: 1) Dose-response curve of CCh-induced tonic contractions 2) Inhibitory dose-response curve of chloride transport inhibitors and CC blockers on CCh-induced tonic contractions 3) Inhibitory dose-response curve of chloride transport inhibitors and CC blockers on amplitude and frequency of phasic contractions in normal and CYP-OAB bladder SM. The tensions and curves were compared among normal, CYPc40-OAB and CYPc80-OAB bladder tissues. The chloride transport inhibitors included bumetanide (BUM), 4-(2-hydroxyethyl)-1-1- piperazine ethanesulphonic acid (HEPES) without bicarbonate, ethacrynic acid (ETH). CC blockers included  4,4'-diisothiocyano-2,2'-stilbene- disulfonic acid (DIDS), anthracene-9-carboxylic acid (A9C) and niflumic acid (NFA) (All concentration: 10^-8M~1M).

Results: 1) CCh could trigger tonic contraction on isolated rat bladder SM in control, CYPc40 and CYPc80 groups in a concentration dependent manner. When compared with control group, the contractile tensions were significantly lower in CYPc40 and CYPc80 groups. 2) Pretreatment with BUM, HEPES without bicarbonate, or ETH could significantly suppress the CCh-induced contractility in control, CYPc40 and CYPc80 groups in a concentration dependent manner (all p<0.01). Pretreatment with DIDS, A9C or NFA could also significantly reduce the CCh elicited contractile response in control, CYPc40 and CYPc80 groups in a concentration dependent manner (all p<0.01). A greater percentage of inhibition in CCh-induced contraction could be observed in OAB (CYPc40 and CYPc80) groups than in control group using all the chloride transport inhibitors and CC blockers at various concentrations. 3) Both the amplitude and frequency of spontaneous phasic detrusor contractions could be reduced by treatment of BUM, HEPES without bicarbonate, ETH, DIDS, A9C or NFA in a concentration dependent manner in control, CYPc40 and CYPc80 groups. However, there is no significant difference in percentage of inhibition in amplitude and frequency of phasic detrusor contraction between control and OAB groups.

Conclusions: The CCh-induced tonic bladder contractions diminished in OAB rats. Both the CCh-induced tonic bladder contractions and phasic detrusor contractions in control and OAB bladder SM strips could be significantly inhibited by various chloride transport inhibitors and CC blockers. The CCh-induced tonic bladder contraction is more susceptible to the inhibition of these reagents in OAB than in control groups, suggesting the pathophysiological evidence for calcium-activated chloride channel in the regulation of OAB bladder SM tone.