Voltage‐operated Ca ^{2 +} currents and Ca ^{2 +} ‐activated Cl ^– currents in single interstitial cells of the guinea‐pig prostate

Abstract

Objective To investigate the expression of ‘ T ‐type’ and ‘ L ‐type’ voltage‐operated Ca 2 + 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 ( PIC s) dispersed using collagenase. Results In contrast to prostatic myocytes, PIC s under voltage clamp and filled with K + (130 m m ) 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 C s + ‐filled PIC s evoked an inward current at potentials positive to −60 mV, which peaked in amplitude near 0 mV. This inward current increased when B a 2+ (5 m m ) replaced the external Ca 2 + (1.5 m m ) and displayed a variable sensitivity to the inhibitory actions of conditioning depolarisations to −40 mV applied before the test depolarisation or to 1 μ m nifedipine, the ‘ L ‐type’ Ca 2 + channel blocker. A residual inward current recorded in nifedipine was blocked by 10 μ m Ni 2 + . 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 μ m ) and blocked by Ba 2 + or a conditioning depolarisation. Conclusion PIC s express both a small ‘ T ‐type’ Ca 2 + channel current ( I Ca ) and a large ‘ L ‐type’ I Ca . Ca 2 + influx through ‘ T ‐type’ I Ca was an essential trigger for the activation of a Ca 2 + ‐activated C l – ‐selective current. The dependence of PIC Ca 2 + 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.