Spontaneous contractions of intestinal smooth muscle re-aggregates from the new-born rat triggered by thromboxane A2

Isolated smooth muscle cells from the small intestine of new-born rats were prepared by enzymatic digestion. These cells re-aggregate after 1 day in culture to clusters. The re-aggregates show spontaneous rhythmical contractions at 37 degreesC with a frequency (13.1 +/- 0.8 min(-1), n = 49), which is similar to that of the intact smooth muscle layer. The cholinergic agonist carbachol (5 x 10(-5) mol l(-1)) caused an increase in the frequency of the spontaneous contractions often ending in a permanent contraction. A similar effect was achieved with the thromborane A(2) (TXA(2)) agonist, U-46619 (10(-5) mol l(-1)). In contrast, both the TXA(2) receptor blocker, Bay u3405 (5 x 10(-4) mol l(-1)), as well as the Ca2+ channel blocker, verapamil (5 x 10(-5) mol l(-1)), suppressed the spontaneous contractions. The observed contractility was insensitive against the neuronal blocker tetrodotoxin (10(-6) mol l(-1)) These analyses of video images were supported by the measurement of relative changes in the intracellular Ca2+ concentration with the Ca2+-sensitive dye, fura-2. Spontaneous contractions were paralleled by spikes in the intracellular Ca2+ concentration, which were abolished by Bay u3405 but stimulated by U-46619 or carbachol. In summary, these results obtained at re-aggregates of intestinal smooth muscle cells support the hypothesis of a role of TXA(2), in che generation of spontaneous intestinal smooth muscle contractions in vitro.