Mechanism of mechanical inhibition of smooth muscle by ouabain.
1 Ouabain (10 mug/ml) caused an initial increase followed by a decrease in tension in guinea-pig taenia coli bathed in normal sodium and potassium containing medium. 2 The excitatory effect of ouabain was prevented by the elevation of extracellular potassium while the inhibitory effect was abolished in the absence of sodium in the bathing medium. 3 In the presence of sodium, the inhibitory effect of ouabain disappeared when the drug was washed out, but in the presence of lithium (which is not extruded by the Na-K pump) the inhibition was not abolished. 4 The inhibitory effect of ouabain was accompanied by an increase in tissue Na and a decrease in tissue K concentration. The increase in intracellular [45Ca] which occurred when extracellular [k] was varied, was also reduced by ouabain. 5 It is concluded that a high intracellular level of sodium inhibits contractions in visceral smooth muscle probably by a mechanism involving decreased Ca influx.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D003106:Colon / Q000187:drug effects; D003864:Depression, Chemical; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology
D010042:Ouabain; D008094:Lithium; D012964:Sodium; D011188:Potassium; D002118:Calcium