• urinary bladder;
  • interstitial cells of Cajal;
  • calcium current


To determine whether there are inward currents in interstitial cells (IC) isolated from the guinea-pig detrusor and if so, to characterise them using the patch-clamp technique and pharmacological agents.


Using the whole-cell patch-clamp technique, inward currents were studied in IC enzymatically isolated from the detrusor of the guinea-pig bladder. Currents were evoked by stepping positively from a holding potential of − 80 mV.


Outward K+ currents were blocked by Cs+ internal solution to reveal inward currents, which activated at voltages more positive than − 50 mV, peaked at 0 mV, reversed near + 50 mV and were half-maximally activated at − 27 mV. The inward currents showed voltage-dependent inactivation and were half-maximally inactivated at − 36 mV. Fitting the activation and inactivation data with a Boltzmann function revealed a window current between − 40 mV and + 20 mV. The decay of the current evoked at 0 mV could be fitted with a single exponential with a mean time-constant of 88 ms. Replacing external Ca2+ with Ba2+ significantly increased this to 344 ms. The current amplitude was augmented by Ba2+, and by Bay K 8644. Inward currents were significantly reduced by 1 µm nifedipine, across the voltage range, but the blockade was more effective on the current evoked at 0 mV than that evoked by a step to − 20 mV, perhaps indicating voltage-dependence of the action of nifedipine or another component of inward current. Increasing the concentration of the drug to 10 µm caused no further significant reduction either at 0 mV or at −20 mV. However, in the presence of 1 µm nifedipine the latter current was significantly reduced by 100 µm Ni2+. Both currents were significantly reduced in Ca2+-free solution.


IC from the guinea-pig detrusor possess inward currents with typical characteristics of L-type Ca2+ current. They also have a component of inward Ca2+ current, which was resistant to nifedipine, but sensitive to Ni2+. Further work is needed to characterise the latter conductance.