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Intracellular recordings were made from myenteric interstitial cells of Cajal (ICC-MY) distributed in the guinea-pig gastric antrum to investigate the properties of unitary potentials. In most cells studied, pacemaker potentials with initial fast transient and following plateau components were generated periodically, and intervals between the potentials were quiescent. However, there were few cells (less than 5% of cells examined) which showed discharge of unitary potentials spontaneously in the intervals between pacemaker potentials. The amplitude and frequency of unitary potentials appeared to be random variables, as observed in isolated circular smooth muscle bundles of the guinea-pig gastric antrum. BAPTA-AM (an intracellular Ca2+ chelator) or papaverine (a non-selective phosphodiesterase inhibitor) reduced the discharge frequency of unitary potentials, with associated decrease in the frequency of pacemaker potentials. These agents finally abolished both unitary potentials and pacemaker potentials. In preparations showing no detectable generation of unitary potentials, depolarization of the membrane with high-K solution ([K+]o = 10.6 mM) elicited generation of unitary potentials during intervals between pacemaker potentials. Pinacidil (an opener of K(ATP)-channels) hyperpolarized the membrane and increased the frequency and amplitude of unitary potentials with no alteration to the relationship between the amplitudes of unitary potentials and their half-widths. These results suggest that the elevation of intracellular Ca2+ concentration is causally related to the generation of unitary potentials in pacemaker cells. They are consistent with the proposition that the depolarization produced by a burst of unitary potentials triggers the primary component of pacemaker potentials in ICC-MY, which induces a release of Ca2+ from inositol 1,4,5-trisphosphate (IP3)-sensitive internal stores and then activates Ca2+-sensitive Cl- -channels to form the plateau component. Similarities and differences in unitary potentials between circular muscle and pacemaker cells are discussed.

Properties of Unitary Potentials Recorded from Myenteric Interstitial Cells of Cajal Distributed in the Guinea-Pig Gastric Antrum