Voltage-operated Ca2+ currents and Ca2+-activated Cl- currents in single interstitial cells of the guinea-pig prostate

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 depolarisation when under current clamp. Depolarisation 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 depolarisations to -40 mV applied before the test depolarisation or to 1 mu M nifedipine, the 'L-type' Ca2+ channel blocker. A residual inward current recorded in nifedipine was blocked by 10 mu M 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 mu M) and blocked by Ba2+ or a conditioning depolarisation. Conclusion PICs express both a small 'T-type' Ca2+ channel current (I-Ca) and a large 'L-type' I-Ca. Ca2+ influx through 'T-type' I-Ca was an essential trigger for the activation of a Ca2+-activated Cl--selective current. The dependence of PIC Ca2+ signalling on 'T-type' and 'L-type' I-Ca is unique compared with other interstitial cells of the urogenital tract and may well be pharmaceutically exploitable.