Non-co-ordinate development of β-adrenergic receptors and adenylate cyclase in chick heart

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Abstract
Properties of .beta.-adrenergic receptors and of their interaction with adenylate cyclase were studied in the chick myocardium during embryogenesis. Between 4.5-7.5 days in ovo, the number of receptors as determined by (-)-[3H]dihydroalprenolol ([3H]DHA) binding is constant at .apprx. 0.36 pmol receptor/mg protein. By day 9 the density decreased significantly to 0.22 pmol and at day 12.5-13.5 the number was 0.14-0.18 pmol. This number did not change further up to day 16. The same results were obtained with guanosine 5''-[.beta.,.gamma.-imido]triphosphate (p[NH]ppG) added to the assay mixtures. There was no significant change in receptor affinity for the antagonist [3H]DHA between days 5.5-13. Despite the decrease in numbers of .beta.-adrenergic receptors, there was no change in basal, p[NH]ppG-, isoprenaline- or isoprenaline-plus-p[NH]ppG-stimulated adenylate cyclase activity between days 3-12 of development. .beta.-Adrenergic receptors and adenylate cyclase are not coordinately regulated during early embryonic development of the chick heart. Some of the .beta.-adrenergic receptors present very early in the ontogeny of cardiac tissue appear not to be coupled to adenylate cyclase, since their loss is not reflected in decreased activation of the enzyme.