Reciprocal Expressions of α₁- and β-Adrenergic Receptors, but Constant Expression of Glucagon Receptor by Rat Hepatocytes during Development and Primary Culture

Abstract

The stimulations of cyclic AMP formation and adenylate cyclase activity by glucagon and isoproterenol were both found to be highest in neonatal rat hepatocytes and to decrease during development. Adult hepatocytes still showed a considerable response to glucagon, but a negligible response to isoproterenol. The decrease in cyclic AMP formation during development can be explained in the case of the response to β-adrenergic agonist as due to decrease of its receptor number, judging from binding of [¹²⁵I] iodocyanopindolol to purified plasma membranes. But in the case of the glucagon response, the decrease in the response may be due to change of post-receptor components of the adenylate cyclase system, because the receptor number tended to increase during development, as shown by binding of [¹²⁵I] iodoglucagon. Similarly, α₁-adrenergic receptors increased in number during development, but their IC₅₀ value did not change, as measured by binding of [³H] prazosin to plasma membranes. Previous studies on primary cultures of adult rat hepatocytes showed that the β-adrenergic response and its receptor number increased markedly during short-term culture (Nakamura, T., Tomomura, A., Noda, C., Shimoji, M., & Ichihara, A. (1983) J. Biol. Chem. 258, 9283-9289). However, in this work the amount of α₁-adrenergic receptor of adult rat hepatocytes was found to decrease by one third during 1-2 days culture. Therefore, changes of α₁- and β-adrenergic receptors during development of rat liver and during primary culture of adult rat hepatocytes were reciprocal, although the directions of change in the two conditions were opposite. The additions of various hormones to primary cultures of adult rat hepatocytes did not affect the reciprocal changes of adrenergic receptors, suggesting that these hormones did not regulate the changes of the receptors.