Gap junctions are present at the coupling of different cell types within the urinary bladder [1]. Detrusor, the smooth muscle of the bladder, displays contractile phasic activity (PA) during urine storage. This PA could be facilitated by cell-to-cell communication e.g. via gap junctions. Increased PA may result in pathologies. Hence, we characterize the effects of known gap junction blockers: isomers 18α- and 18β-glycyrrhetinic acid (18α-,18β-GA) and carbenoxolone (CBX) [2] on intact (including mucosa) and mucosa-denuded detrusor bladder tissue. Bladders were isolated from male Wistar rats (P19-24 days) killed by CO2 under UK Schedule 1 regulations. Denuded and intact tissue strips (5-8mm long) were placed in superfusion tissue organ baths, maintained in oxygenated Krebs buffer at 37°C and tied to a tension transducer to a resting tension of 1g. In the absence of measureable spontaneous PA in intact strips and in all denuded strips, 1µM carbachol (CCh) was used to induce PA. Changes in the contractile force were measured (ADInstruments) throughout the control period, single dose drug exposure and a washout period, each 30min. 1,10 and 30µM 18β-GA; 30µM 18α-GA and 50µM CBX were used. The effect of a drug or drug vehicle on PA was investigated by measuring the amplitude (g per mg tissue) and frequency of PA (number of contractions during 5 min). Data show mean percentage change ± SEM from at least 7 strips from at least 6 animals (two-tailed paired t-test, p<0.05 was considered significant). Amplitude of bladder tissue CCh-induced PA decreased with increasing concentrations of the 18β-GA. In intact tissue 10µM 18β-GA decreased PA amplitude by 15.6 ± 4.7% (p < 0.05). Amplitude decreased by 33.3 ± 4.9% (p < 0.001) and 32.7 ± 3.4% (p < 0.01) with 30µM 18β-GA and 18α-GA, respectively. PA frequency increased by 20.1 ± 5.8% (p < 0.01) at 30µM 18β-GA. The effect of 18β-GA was stronger in denuded detrusor strips. 10µM 18β-GA decreased PA amplitude by 36.1 ± 2.0% (p < 0.001) and 30µM 18β-GA by 42.6 ± 9.1% (p < 0.01). At 30µM 18β-GA PA frequency increased by 51.2 ± 24.0% (p < 0.05). In contrast, 50µM CBX showed a trend of increasing PA amplitude in both denuded and intact strips, while simultaneously decreasing PA frequency. The frequency of contractions in intact strips decreased by 26.5 ± 6.1% (p < 0.01). Preliminary data on spontaneous, not CCh-induced PA suggest the effects of both drugs are less pronounced in unstimulated tissue. 18β-GA increased frequency and decreased amplitude of CCh-stimulated bladder tissue PA, with a stronger effect in denuded strips. CBX decreased PA frequency – a different observation to 18β-GA – and showed a trend in increasing PA amplitude – opposite to 18β-GA effect. This unexpected difference will be further characterized.