Changes in the fast component of the rabbit vena cava contraction after repeated stimulation by noradrenaline(NA).
The fast component of the rabbit vena cava contraction after repeated stimulation by NA was investigated. Experimental conditions which are known to increase the cellular calcium content led to an increase in contraction amplitude. Transient incubation between stimulations in a solution with high [Ca2+], in a solution with high [K], in a K+-free solution or in a solution containing ouabain is an example of such conditions. When the duration of a singly stimulus in a train of NA stimuli was prolonged the following contraction decreased. With increasing incubation time in Ca2+-free solution the maximum of contraction amplitude decreased far more after repeated stimulation than after a single stimulus. The results allow the interpretation that the fast component of the rabbit vena cava contraction which is induced by NA is related to the cellular calcium content. Moreover the results suggest that only a fraction of the cellular calcium is releasable by NA and that Ca2+-free conditions and/or NA exposure deplete this fraction.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D013268:Stimulation, Chemical; D014684:Venae Cavae / Q000187:drug effects
D010042:Ouabain; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine