Manifestation of latent alpha-excitatory response in the canine tracheal smooth muscle preparation--relation to basal tone.
Alpha-adrenergic contractile response of the tracheal smooth muscle preparation isolated from young adult dogs was investigated. When the basal tone of the preparation was elevated by spasmogens, methacholine, K+, etc., in the presence of 1 microM propranolol, norepinephrine and phenylephrine caused contraction of the preparation. Isoproterenol did not. The contraction was specifically antagonized by phentolamine. The height of contraction caused by alpha-stimulants depended on the height of basal tone. The relationship of them was essentially the same whether methacholine on K+ was used as spasmogen, and if the Ca ion concentration in Krebs' solution was reduced to 0.1 mM. It was concluded that the tracheal smooth muscle of young adult dogs which is usually insensitive to alpha-stimulants responds to them when the basal tone is elevated by spasmogens, and it was suggested that an elevated intracellular free-Ca ion level contributed to this phenomenon.
D000818:Animals; D002118:Calcium / Q000502:physiology; D002395:Catecholamines / Q000502:physiology; D004285:Dogs; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008688:Methacholine Compounds / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D014132:Trachea / Q000502:physiology*
D002395:Catecholamines; D008688:Methacholine Compounds; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011188:Potassium; D002118:Calcium; D004837:Epinephrine