Age influences responses of rat isolated aorta and pulmonary artery to the calcium channel agonist, Bay K 8664, and to potassium and calcium.
Responses of isolated ring preparations of aorta and pulmonary artery from young (2 months) and aged (19-21 months) rats have been obtained to five contractile agents with differing mechanisms of action. The potencies (negative log EC50 values), but not the absolute maximum contractions (mN/mm2), for potassium, calcium (in K+-depolarized preparations), and the calcium channel activator, Bay K 8644, were all reduced in preparations from aged, compared with young, rats, and this reduction was more pronounced in aorta than in pulmonary artery. In contrast, the age of the rats had no influence on responses (potency or maximum contractions) to caffeine or the ionophore, A23187, indicating that the contractile ability of the preparations per se was retained in the aged rats. Aortic preparations from young rats contracted to Bay K 8644 without prior depolarization, whereas those from aged rats required partial depolarization (with 6 mM KCl) before consistent contractile responses to Bay K 8644 could be obtained. It is concluded that the influence of age on vascular contractions varies (a) between contractile agents, depending on their mechanisms of action and (b) between blood vessel types. To explain the reduced potencies of Bay K 8644, potassium, and calcium in aorta from aged rats, it is postulated that the resting membrane potential may be more negative in the preparations from the aged rats.
Wanstall
J C
JC
Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Brisbane, Australia.
O'Donnell
S R
SR
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000375:Aging / Q000502:physiology*; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002122:Calcium Chloride / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains
D000001:Calcimycin; D002110:Caffeine; D011189:Potassium Chloride; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002122:Calcium Chloride; D011188:Potassium; D002118:Calcium