EFFECTS OF POTASSIUM, ACETYLCHOLINE, CARBACHOL AND HISTAMINE ON Na²² MOVEMENTS IN ILEAL SMOOTH MUSCLE

¹ Department of Pharmacology, Medical College of Virginia, Richmond, Virginia

The effects of several stimulatory agents upon Na²² uptake in longitudinal smooth muscle isolated from guinea-pig ileum were measured. NaM uptake was not altered by raising the potassium concentration of the Tyrode's solution to 80 mM but was markedly increased by substitution of K for the nonradioactive Na in the bathing solution. The largest increases in Na²² uptake obtained with acetyicholine, carbachol or histamine occurred when muscles were incubated in 22 prior to a brief exposure to one of these stimulatory agents. The increased 22 uptake was seen mainly as part of the slow washout component. An increase in total content was also induced by acetylcholine, carbachol and histamine. The magnitude of contractile responses to various stimulatory agents was not inhibited either by ouabain (even though muscle content was increased) or by substitution of for Na²². It appears that Na²² movements and changes in cellular gradients can be dissociated from tension responses under some conditions. Thus, movements and contractions induced by stimulatory agents may not always occur in sequence in ileal smooth muscle but, instead, can be parallel and largely independent cellular responses.