MANIFESTATION OF LATENT ALPHA-EXCITATORY RESPONSE IN THE CANINE TRACHEAL SMOOTH-MUSCLE PREPARATION - RELATION TO BASAL TONE

  • 1 January 1981
    • journal article
    • research article
    • Vol. 251  (2) , 205-216
Abstract
.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 .mu.M propranolol, norepinephrine, epinephrine 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. Their relationship was essentially the same whether methacholine or K+ was used as spasmogen and if the Ca ion concentration in Krebs'' solution was reduced to 0.1 mM. 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 apparently an elevated intracellular free-Ca ion level contributed to this phenomenon.