OBJECTIVE: * To investigate the expression of T-type and L-type voltage-operated Ca2+ channels in single interstitial cells of the guinea pig prostate. MATERIAL AND METHODS: * Whole-cell and perforated patch clamp techniques were applied to prostatic interstitial cells (PICs) dispersed using collagenase. RESULTS: * In contrast to prostatic myocytes, PICs under voltage clamp and filled with K+ (130 mM) were distinguished by the absence of a voltage-operated transient outward K+ current or spike discharge upon membrane depolarization when under current clamp. * Depolarization of Cs+ -filled PICs evoked an inward current at potentials positive to -60 mV which peaked in amplitude near 0 mV. This inward current increased when Ba2+ (5 mM) replaced the external Ca2+ (1.5 mM) and displayed a variable sensitivity to the inhibitory actions of conditioning depolarizations to -40 mV applied before the test depolarization or to 1 muM nifedipine, the L-type Ca2+ channel blocker. * A residual inward current recorded in nifedipine was blocked by 10 muM Ni2+ . Cs+ -filled PICs also displayed a slowly-inactivating outward current that was little affected by nifedipine, reduced by the Cl- channel blocker, niflumic acid (10 muM) and blocked by Ba2+ or a conditioning depolarization. CONCLUSION: * PICs express both a small T-type Ca2+ channel current (ICa ) and a large L-type ICa . * Ca2+ influx through T-type ICa was an essential trigger for the activation of a Ca2+ -activated Cl- selective current. * The dependence of PIC Ca2+ signalling on T- and L-type ICa is unique compared to other interstitial cells of the urogenital tract and may well be pharmaceutically exploitable.