AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 6 1430-R1438, Copyright © 1993 by American Physiological Society
Adaptations of myocardial beta-adrenergic receptor complex in hibernating marmots
S. A. Morris, G. Florant, M. Saxon, G. Chen and J. P. Bilezikian
Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Properties of marmot (Marmota flaviventris) myocardial beta-adrenergic
receptor complex (beta-AR) were evaluated during hibernation (H), in summer
(S) animals, and in animals aroused from hibernation (C). The results
obtained for S and C animals were identical, and only the results for C
animals are shown. In H-animal myocardial membrane preparations assayed at
37 degrees C, isoproterenol-dependent adenylate cyclase activity (ACA) was
consistently higher, whereas the synergistic contribution of
5'-guanylylimidodiphosphate [Gpp(NH)p] in this reaction was reduced. When
assayed at 10 degrees C, only the ACA in H animals responded to the
combination of isoproterenol and Gpp(NH)p. In contrast, at 10 degrees C,
ACA in response to Gpp(NH)p alone is essentially equal in H and C animals.
Hibernation did not change myocardial beta-AR receptor density or affinity.
In contrast, analysis of isoproterenol displacement of
[125I]iodocyanopindolol revealed that the proportion of beta-AR in the
high-affinity state was substantially greater in H than in C animals, and
this relationship was retained even in the presence of Gpp-(NH)p. In an
evaluation of the role of the GTP binding proteins that couple the beta-AR
to the effector adenyl cyclase, we determined that there was no change in
the cholera toxin- or pertussis toxin-dependent ADP ribosylation patterns.
Immunochemical detection of the individual GTP binding proteins revealed no
change in the levels of G alpha i1, G alpha i2, or G alpha i3. In contrast,
we observed a hibernation-associated decrease in G alpha o associated with
the plasma membrane-enriched particulate fraction. (ABSTRACT TRUNCATED AT
250 WORDS)
