Electrical characterization of interstitial cells of Cajal-like cells and smooth muscle cells isolated from the mouse ureteropelvic junction

PURPOSE: We characterized membrane currents in smooth muscle cells and interstitial cells freshly isolated from the mouse ureteropelvic junction. RESULTS: Membrane depolarization of single smooth muscle cells evoked a complex K(+) selective outward current consisting of a rapidly activating 4-aminopyridine sensitive transient outward current, followed by a more slowly developing outward current that was decreased by blockers of large conductance Ca(2+) activated K(+) channels. In contrast, membrane depolarization of stellate interstitial cells evoked a slowly developing outward current that did not arise from the opening of transient outward current or large conductance Ca(2+) activated K(+) channels. Under current clamp interstitial cells showed random fluctuations of membrane potential and occasional large, long lasting depolarizations. Under voltage clamp interstitial cells showed high frequency spontaneous transient inward currents that often occurred in bursts to sum and produce long lasting large inward currents. Large inward currents had reversal potentials of almost -10 mV if the Nernst potential for Cl(-) was set at -4 or -78 mV. They were little affected by the Cl(-) channel blockers DIDS (4,4 -diisothiocyanostilbene-2,2 -disulphonic acid) and niflumic acid. CONCLUSIONS: We speculate that single stellate interstitial cells are c-Kit positive interstitial cells of Cajal-like cells viewed in intact tissue, which generate cationic selective spontaneous transient inward currents that sum to form large inward currents. In the absence of a proximal pacemaker drive these interstitial cells of Cajal-like cells could well trigger contraction in neighboring smooth muscle cell bundles in the ureteropelvic junction.