Electrical activity of an intestinal epithelial cell line: hyperpolarizing responses to intestinal secretagogues

Cultured epithelial cells (Intestine 407) derived from fetal human small intestine exhibited spontaneous oscillations of membrane potential between the resting level of about -20 mV and the activated level of about -75 mV. The cells were hyperpolarized to the latter level in response to mechanical or electrical stimuli. The hyperpolarizing responses were also elicited by the application of intestinal secretagogues: acetylcholine, histamine, serotonin and vasoactive intestinal polypeptide (VIP). The spontaneous oscillation of membrane potential became prominent and long-lasting in the presence of acetylcholine, histamine, serotonin or VIP. These secretagogue-induced responses were mediated by individual independent receptors on the cell membrane. Muscarinic receptors were responsible for the acetylcholine response, and H1-receptors for the histamine response. The cells also responded with a slow hyperpolarization to calcium ionophore A23187, which is known to induce intestinal secretion. The spontaneously occurring hyperpolarizing responses and those induced by stimuli were both due to an increase in the K+ conductance of the cell membrane. Since acetylcholine, histamine, serotonin and A23187 are known to promote mobilization of cellular Ca2+ ions in intestinal secretory cells, it is hypothesized that these electrical activities of the cell are closely related to the receptor stimulation which leads to the Ca2+-mediated intestinal secretion.