Mechanisms controlling Ca signalling in visceral and vascular smooth muscle cells can differ but interpretation is complicated because of differences in the type of tissue or vessel studied as well as experimental conditions. In the present study we have overcome these problems by using in situ imaging of Fluo-4 loaded ureters, isolated from humanely killed guinea pigs, to investigate and compare mechanisms controlling Ca signalling in visceral (ureteric) and vascular (ureteric arteriolar) smooth muscle cells in the same preparation under identical experimental conditions.The ureteric myocytes were electrically coupled and when stimulated by electrical field (EFS) via focal electrode with rectangular pulses (5-7V, 100msec in duration) with 40 s interval generated intercellular/inter-bundular fast propagating (6-7cm/sec), regenerative Ca waves. The wave could be initiated in any part of the ureter and propagated in all directions from the point of stimulation. Simultaneous recording of electrical activity and Ca imaging revealed that the intercellular Ca waves evoked by EFS were associated with action potentials, which were abolished in Ca-free solution or nifedipine. EFS did not induce any propagating intercellular Ca wave in terminal arterioles. High-K (60 mM) stimulation produced a sustained Ca rise in both types of cells which was blocked by Ca-free solution or nifedipine. Phenylephrine (PhE, 10 µM) stimulated both ureteric and arteriolar myocytes. In the ureteric bundles it produced 1.7±0.1 times increase in the duration of the Ca transients but was ineffective in Ca-free solution. In contrast, vascular myocytes responded with asynchronous Ca oscillations in the form of intracellular Ca waves, travelling at a speed of 30-60µm/sec. These Ca waves were highly resistant to nifedipine or removal of extracellular Ca (Ca free, 2 mM EGTA for 60-90min)(n=17). Both types of cells produced spontaneous Ca sparks which were potentiated by low concentrations of caffeine and abolished by ryanodine. Ryanodine increased the excitability in ureteric cells but had no effects on PhE induced Ca oscillations in the vascular myocytes. Inhibition of the SR Ca-ATPase by cyclopiazonic acid (20 µM) increased excitability of the ureteric cells but abolished PhE –induced Ca oscillations in vascular myocytes. 2-APB (50 µM) (an inhibitor of IP3 signalling) had no effects on Ca signalling in ureteric cells but abolished PhE –induced Ca oscillations in vascular myocytes. These data suggest that Ca influx via L-type Ca channels, mediated by the action potential, is the main mechanism controlling Ca signalling in ureteric myocytes. In contrast Ca release from the SR mediated by IP₃Rs channels is the main mechanism controlling Ca signalling in vascular myocytes in the ureteric microvessels.