Effects of verapamil, sodium nitroprusside, tetrodotoxin and caffeine on the electrical transmural stimulation induced contraction in the reticular groove smooth muscle of adult cattle.

The effect of electrical transmural stimulation (ETS) on smooth muscle strips in the floor of reticular groove of adult cattle was studied. The mechanical activity of the muscle strips was recorded isometrically. ETS (4 ms, 5 s, supramaximal voltage) caused frequency dependent (2-30 Hz) contractions of this smooth muscle. An increase in cytoplasmatic free calcium concentration can be achieved by release of the cation from intracellular store sites or by an influx of extracellular Ca2+ through calcium channels. The contractile response of the muscle strips was inhibited about 66% when it was incubated in a calcium-free EGTA-containing solution. The excitatory effect of ETS was not antagonized by verapamil (10(-6) mol/l), sodium nitroprusside (10(-6) mol/l) or tetrodotoxin (10(-6) mol/l). The electrically-evoked contraction was inhibited strongly (92%) by caffeine (30 mmol/l). The contractions of the smooth muscle from the reticular groove smooth muscle are dependent on the concentration of free calcium in the cell cytosol. This response was intracellular Ca2+ ion dependent.