Interstitial cells of Cajal generate spontaneous transient depolarizations in the rat gastric fundus.

Intracellular recordings were made from isolated circular muscle bundles of rat gastric fundus. The majority of cells generated an ongoing discharge of electrical activity that were <or=10 mV in amplitude (unitary potentials). A second pattern of electrical activity was recorded in less than 1% of all impalements. This electrical activity was characterized by high frequency, large amplitude spontaneous transient depolarizations (STDs) with a maximum rate of rise (dV/dt(max)) of 0.5 V/s. Injection of the fluorescent dye propidium iodide into cells and double labeling with an antibody against the Kit receptor revealed that unitary potentials were recorded from circular smooth muscle cells (CSMC), whereas STDs were generated by intramuscular interstitial cells of Cajal (ICC-IM). Sustained injection periods (>15 min) resulted in the spread of dye between CSMC, between ICC-IM, and between CSMC and ICC-IM. Two types of STDs were observed, regularly occurring continuous STDs and irregular noisy bursting STDs. The amplitude of STDs varied between the two types of STDs. Single units summed to develop STDs with a maximum amplitude of 30 mV. Sodium nitroprusside (3 microM) induced membrane hyperpolarization and abolished unitary potentials generated by CSMC. In contrast, the amplitude of STDs generated by ICC-IM was increased with membrane hyperpolarization. Hyperpolarization induced by pinacidil (10 microM) also increased the amplitude of STDs and enhanced dV/dt(max). These observations indicate that STDs generated in ICC-IM spread passively to the adjacent CSMC to evoke the discharge of unitary potentials in the gastric fundus.