Generation of slow waves in membrane potential is an intrinsic property ofinterstitial cells of Cajal

To reveal the unique intrinsic properties of interstitial cells of Cajal (I CC), morphological and electrophysiological characteristics of isolated ICC from the adult mouse small intestine were investigated and compared with t hose of smooth muscle cells. All typical ultrastructural features of in sit u ICC were evident in isolated ICC throughout the isolation procedure and s hort-term culture. With the use of the nystatin perforated patch-clamp tech nique, ICC demonstrated spontaneous voltage oscillations that were not abol ished by hyperpolarization nor by L-type calcium channel blockers. This rhy thmic activity occurred at room temperature at a frequency of 13.9 +/- 11.2 cycles/min, with an amplitude of 13.4 +/- 11.2 mV at membrane potentials f rom -20 to -70 mV. Smooth muscle cells from the same culture only generated voltage-sensitive action potentials above the threshold potential of -35 m V. Hyperpolarization as well as the addition of L-type calcium channel bloc kers abolished the action potentials. In whole cell voltage-clamp recording s from ICC, a large noninactivating outward current was observed to be acti vated (5% threshold) at -49.6 mV with a half-activation voltage of -18.7 mV and slope factor of 9.9 mV. In contrast, in smooth muscle cells, smaller o utward currents with distinctive transient outward currents were present. I n conclusion, the generation of L-type calcium channel blocker-insensitive slow waves in membrane potential is a unique intrinsic property of ICC.