The potentiation of norepinephrine-induced contraction of rabbit aorta by Mg2+ deletion in a Ca2+-free medium.
Residual responses to norepinephrine (NE) in an Mg2+-, Ca2+-free medium with low EGTA (0.1 mM) for 15 min were potentiated following preincubation of rabbit aortas in Mg2+-free medium for 60 min. Responses to Ca2+ in a Ca2+-free medium with nifedipine and NE were not affected under a similar Mg2+-free condition. Nifedipine, theophylline, dibutyryl cAMP, 8-bromo-cGMP, methylene blue, La3+ or vanadate did not affect the residual response or the potentiation. However, high EGTA (1 mM) inhibited both the residual response and the potentiation. The residual response to NE was not potentiated following incubation in Mg2+-, Ca2+-free medium for 60 min. These results suggest that, in the rabbit aorta, Mg2+ deletion from the medium selectively potentiates the residual response to NE in a Ca2+-free medium without any effect on the response due to Ca2+-influx through receptor-operated channels. This potentiation does not appear to be related to either the levels of cAMP and cGMP or the activity of an Mg2+-dependent, Ca2+-ATPase.
Morikawa
M
M
Department of Pharmacology, John A. Burns School of Medicine, University of Hawaii, Honolulu.
Satake
N
N
Hester
R K
RK
Shibata
S
S
D000818:Animals; D001011:Aorta / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000493:pharmacokinetics; D004533:Egtazic Acid / Q000494:pharmacology; D006571:Heterocyclic Compounds / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D011817:Rabbits; D014638:Vanadates / Q000494:pharmacology
D006571:Heterocyclic Compounds; D014638:Vanadates; D004533:Egtazic Acid; D007811:Lanthanum; D008274:Magnesium; D002118:Calcium; D009638:Norepinephrine