Abstract
The effect of orthovanadate on the response caused by the beta-adrenergic receptor agonist isoprenaline and on the ATP response were investigated by measuring potential changes and changes in the contractile state of smooth muscle cells of guinea-pig taenia caeci at 35 degrees C using the sucrose-gap method. The contraction evoked by carbachol (10(-7) M) or potassium (15 mM) was not modified by orthovanadate (1.0 mM). The hyperpolarization evoked in smooth muscle cells by ATP (0.4 mM) was affected to some extent by orthovanadate (1.0 mM), but was not modified in the absence of extracellular calcium. The hyperpolarization caused by isoprenaline (3 X 10(-6) M), however, was inhibited completely both in the presence and absence of calcium. These results are consistent with the view that isoprenaline activates calcium extrusion from the smooth muscle cells, a process being electrogenic in nature.
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