Abstract
To reveal the unique intrinsic properties of interstitial cells of Cajal (ICC), morphological and electrophysiological characteristics of isolated ICC from the adult mouse small intestine were investigated and compared with those of smooth muscle cells. All typical ultrastructural features of in situ ICC were evident in isolated ICC throughout the isolation procedure and short-term culture. With the use of the nystatin perforated patch-clamp technique, ICC demonstrated spontaneous voltage oscillations that were not abolished by hyperpolarization nor by L-type calcium channel blockers. This rhythmic 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 from -20 to -70 mV. Smooth muscle cells from the same culture only generated voltage-sensitive action potentials above the threshold potential of -35 mV. Hyperpolarization as well as the addition of L-type calcium channel blockers abolished the action potentials. In whole cell voltage-clamp recordings from ICC, a large noninactivating outward current was observed to be activated (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 outward currents with distinctive transient outward currents were present. In conclusion, the generation of L-type calcium channel blocker-insensitive slow waves in membrane potential is a unique intrinsic property of ICC.
Highlights
interstitial cells of Cajal (ICC) and smooth muscle cells derived from the isolation procedure appeared as contracted spindles
Identification of ICC by phase-contrast microscopy was based in part on their significantly darker appearance compared with other cells (Fig. 1)
The ICC were frequently found in close proximity to smooth muscle cells, with processes terminating onto smooth muscle cells
Summary
With the use of the nystatin perforated patch-clamp technique, ICC demonstrated spontaneous voltage oscillations that were not abolished by hyperpolarization nor by L-type calcium channel blockers This rhythmic activity occurred at room temperature at a frequency of 13.9 Ϯ 11.2 cycles/min, with an amplitude of 13.4 Ϯ 11.2 mV at membrane potentials from Ϫ20 to Ϫ70 mV. Action potentials have been shown to occur in isolated smooth muscle cells [2, 3] and can be distinguished from slow wave activity. Action potentials can increase in duration and can assume a slow wave-like appearance [34] This [17] remains susceptible to L-type Ca2ϩ channel blockers and disappears when the membrane potential is brought below the voltage threshold [33]
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