title: Effect of full agonists following calcium deprivation in rat vas deferens.
abstract: The contractile effects of maximum doses of adrenaline, noradrenaline, methacholine, acetylcholine, serotonin and barium chloride were studied following substitution of a medium without calcium for the normal nutrient solution. Except for the last agonist, the effects fall to about 10% within the first 3 min with prompt return to normal value upon reintroduction of regular fluid. This recovery is, however, slower if the previous incubation in Ca-free solution is prolonged. When barium chloride is used in a calcium-free medium, the maximum height of contractions falls exponentially at a t1/2 of about 180 min. This decay can be accelerated by giving successive 5-min doses of the agonist or by using EDTA. It is hypothesised that excitation--contraction  coupling in rat vas deferens depends on at least two different calcium sources: a deep site associated with the effects of barium, and a superficial one, related to the other agonists. To explain the slow recovery after prolonged calcium lack, a third compartment in series with the latter is suggested. No indication is found that the biphasic effects of barium depend on two different calcium pools.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D004492:Edetic Acid / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008688:Methacholine Compounds / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D012701:Serotonin / Q000494:pharmacology; D014649:Vas Deferens / Q000187:drug effects* / Q000502:physiology
chemical_list: D008688:Methacholine Compounds; D001464:Barium; D012701:Serotonin; D004492:Edetic Acid; D000109:Acetylcholine; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine