Contractile force and intracellular Ca2+ during relaxation of canine tracheal smooth muscle.
Muscle strips loaded with the Ca2+ indicator aequorin were studied in vitro to determine the effects of inhibitory stimuli on force and cytosolic free Ca2+. In muscles contracted isometrically with acetylcholine (ACh), 5-hydroxytryptamine (5-HT), carbachol, decreases in muscle force caused by isoproterenol (10(-5) M) or forskolin (10(-5) M) were accompanied by proportional decreases in aequorin luminescence. A similar relationship between decreases in muscle force and aequorin luminescence was observed when muscles were relaxed by stimulating Na+-K+-ATPase activity. These results suggest that the Ca2+ sensitivity of contractile proteins was not decreased during adenosine 3',5'-cyclic monophosphate (cAMP)-dependent relaxation. However, aequorin luminescence did not decrease when muscles contracted by K+ depolarization were relaxed with isoproterenol. Incubation of muscles in forskolin depressed increases in both force and aequorin luminescence in response to 5-HT or ACh. Incubation of muscles in isoproterenol had a similar effect on responses to 5-HT but depressed increases in force without depressing increases in luminescence in response to ACh. Results indicate that under most conditions the reduction of cytosolic Ca2+ plays an important role in the cAMP-dependent relaxation of canine tracheal smooth muscle.
Gunst
S J
SJ
Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
Bandyopadhyay
S
S
D000109:Acetylcholine / Q000494:pharmacology; D000331:Aequorin; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D004285:Dogs; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007537:Isometric Contraction / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014132:Trachea / Q000187:drug effects / Q000502:physiology
D007202:Indicators and Reagents; D005576:Colforsin; D012701:Serotonin; D000331:Aequorin; D010042:Ouabain; D002217:Carbachol; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium