The bladder has dual roles of storage and removal of urine. During the filling phase, low intravesical pressure is achieved through background spontaneous contraction of the smooth muscle. This spontaneous activity is achieved by a complex interaction of nerves, smooth muscle cells and interstitial cells. The aim of the present investigation was to assess the effects of several potassium channel blockers on spontaneous activity in the guinea-pig bladder. Bladders were removed from guinea-pigs, killed by cervical dislocation. Bladders were opened longitudinally; mucosa removed and detrusor strips mounted in organ baths for tension measurements at 35°C. Spontaneous activity typically developed during equilibration of the tissue to an initial tension of 1g. Regular activity was then recorded for at least 30 min and then blockers of various types of potassium channel were added. Application of TEA caused an increase in the amplitude of spontaneous contractions in a concentration-dependent fashion. 10mM TEA increased amplitude from 5.5±1.4mN to 43.8±4.8mN, n=14 tissue strips from 4 animals, p<0.0001, EC50 of 3.31±0.17mM). This was accompanied by a small increase in contraction frequency from 2.0±0.4/min to 3.4±1.2/min (p=0.055). 4-Aminopiridine (0.1mM) increased amplitude from 3.21±1.07mN to 4.96±1.39mN, p=0.023 and increased frequency from 1.6±1.6/min to 3.7±2.7/min, n=18 strips from 5 animals, p=0.0062. The presence of KCNQ channels was investigated using XE991, a blocker of KCNQ channels. 10µM XE991 increased contraction amplitude from 5.1±1.5mN to 13.3±2.8mN, n=11 strips from 3 animals, p=0.0005. The effects on frequency were less clear with 0.5µM increasing frequency from 2.5±0.3/min to 3.00±0.2/min, p=0.104, however, higher concentrations did not further affect frequency. Linopirdine, a less potent analogue of XE991 had similar effects, increasing amplitude from 2.5±0.4 mN to 5.3±1.1mN, n=5 strips from 2 animals, p=0.067. There was little effect on frequency. Application of flupirtine, an opener of KCNQ channels, reversibly decreased contraction amplitude from 11.3±1.4mN to 3.4±0.5mN, n=16 strips from 4 animals, p<0.0001. There was little effect on frequency. The findings of this study show that BK, delayed rectifier and KCNQ channels are all involved in spontaneous contractile activity of the guinea-pig bladder. It is likely that they contribute to repolarisation of the action potential and regulation of the resting membrane potential in smooth muscle cell and interstitial cells. To date, there is little evidence pointing to the presence of KCNQ channels in bladder cells; the present results provide evidence that such channels are present.