Spontaneous contractions of intestinal smooth muscle re-aggregates from the new-born rat triggered by thromboxane A(2)

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 c ulture to clusters. The re-aggregates show spontaneous rhythmical contracti ons at 37 degreesC with a frequency (13.1 +/- 0.8 min(-1), n = 49), which i s similar to that of the intact smooth muscle layer. The cholinergic agonis t carbachol (5 x 10(-5) mol l(-1)) caused an increase in the frequency of t he spontaneous contractions often ending in a permanent contraction. A simi lar 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 u34 05 (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 observe d contractility was insensitive against the neuronal blocker tetrodotoxin ( 10(-6) mol l(-1)) These analyses of video images were supported by the meas urement of relative changes in the intracellular Ca2+ concentration with th e Ca2+-sensitive dye, fura-2. Spontaneous contractions were paralleled by s pikes in the intracellular Ca2+ concentration, which were abolished by Bay u3405 but stimulated by U-46619 or carbachol. In summary, these results obt ained at re-aggregates of intestinal smooth muscle cells support the hypoth esis of a role of TXA(2), in che generation of spontaneous intestinal smoot h muscle contractions in vitro.