Ca²⁺ channel properties in smooth muscle cells of the urinary bladder from pig and human

Ca²⁺ channel properties of pig and human bladder smooth muscle were investigated utilizing standard whole-cell patch clamp techniques. Both the amplitude obtained and the current density of Ca²⁺ channel current evoked by step depolarization were larger in human than in pig myocytes. The inward currents were sensitive to an L-type Ca²⁺ channel antagonist, nifedipine, the effects of which were not significantly different between species. In both species, prior application of ATP (0.1 mM) had no effect on activation of this voltage-sensitive channel current, while a muscarinic receptor agonist, carbachol (0.1 mM), significantly attenuated the amplitude of this current. Furthermore, inclusion of GDP-β-S or Heparin in the pipette abolished or had no effect on the suppression of Ca²⁺ current by carbachol, respectively. These results forward the pig as a good model for the human in detrusor Ca²⁺ channel properties, especially with regard to neural modulation, although voltage-sensitive Ca²⁺ channels seem to make greater contribution in human bladder physiology.