We have previously shown that a layer of c-Kit-immunoreactive interstitial cells lie between the smooth muscle and epithelial layers of the individual acini in the guinea-pig prostate gland (1). These interstitial cells displayed many of the distinguishing features of interstitial cells of Cajal (ICC), the pacemaker cells of the gastrointestinal tract. In this study, we have recorded at least 2 distinct types of spontaneous electrical activity in the stroma of the guinea pig prostate using standard intracellular microelectrode-recording techniques. Prostate glands were removed from humanely killed guinea-pigs (250-350g). Saccular glands were pinned to the bottom of an organ bath, which was subsequently mounted on an inverted microscope stage and perfused with physiological saline solution. Slow waves consisted of a depolarizing transient (14 mV in amplitude) with 1-6 spikes superimposed, pacemaker potentials occurred at the same frequency as slow waves, but were larger in amplitude (40mV), and spontaneous transient depolarizations (STD) occurred irregularly in the presence of the slow wave or pacemaker activity. In the presence of the L-type Ca2+ channel blocker, nifedipine (1μM), the spike potentials superimposed on the depolarising transient of control slow waves were abolished. Other slow wave parameters were not affected (n=18). In contrast, nifedipine had no significant effects on any of the measured parameters of the pacemaker potentials recorded in 5 experiments. In the presence of nifedipine, cyclopiazonic acid (10μM)(n=6) which depletes internal Ca2+ stores by blocking the Ca-ATPase (SERCA) pump on the sarcoplasmic reticulum or the mitochondrial inhibitors, FCCP (10-10μM)(n=4), CCCP (1-10μM)(n=4) or rotenone (1-10μM)(n=3) abolished electrical activity. These results demonstrate that spontaneous electrical activity in the guinea-pig prostate gland is dependent on the release and/or uptake of Ca2+ from intracellular Ca2+ stores and mitochondria. Finally, we speculate that the depolarizing component of slow wave represents the propagated responses of pacemaker potentials arising from our previously identified c-Kit immunoreactive interstitial cells.