Calcium oscillations in freshly dispersed and cultured interstitial cells from canine colon

Spontaneous oscillations in intracellular Ca2+ concentration ([Ca2+]i) and membrane potential were used to monitor rhythmicity in freshly dispersed and cultured interstitial cells (IC) from the canine colon. The frequency of oscillations and responses to a number of channel blockers, agonists, ionic substitutions, and temperature were similar in freshly dispersed and cultured cells. An increase in the amplitude of Ca2+ oscillations after 3-6 days in culture and an increase in the rate of decline of [Ca2+]i in cultured IC were two differences noted between freshly dispersed and cultured cells. The frequency and amplitude of oscillations were a function of extracellular Ca2+ concentrations, and oscillations were abolished when the transmembrane flux of Ca2+ was reduced by nicardipine, La3+, or removal of Ca2+ from the extracellular medium. Oscillations persisted in the presence of ryanodine and ouabain. Lowered temperatures or a reduction in the concentration of Ca2+ in the medium reduced the frequency of spontaneous oscillations. Carbachol and substance P caused a transient increase in [Ca2+]i. Substance P then abolished spontaneous events. ATP and calcitonin gene-related peptide increased the frequency of spontaneous activity. Vasoactive intestinal peptide caused a temporary delay in spontaneous oscillations when added to the medium. Results indicate that freshly dispersed and cultured IC may be useful in studies of the mechanisms of rhythmicity in the gastrointestinal system.