Cell-Density-Dependent Expression of the β-Adrenergic Response by Epidermal Growth Factor (EGF) in Primary Cultures of Adult Rat Hepatocytes

摘要

The effects of epidermal growth factor (EGF) and cell density on the appearance of 0-ndrcncrgic responses were examined in primary cultures of adult rat hepatocytes. The /J-adrenergic response was measured as the aw uy to accumulate cAMP by β2-agonist metaproterenol in monolayers that had been cultured without or with ZUng/mi EGF. Hepatocytes cultured with EGF at a high cell density (1.0 x 105 cells/cm2) showed a relatively lower response to 10/im metaproterenol. In contrast, when cultured at a low cell density (3.3x 104cclls/cnr) with LC.1-, the cells showed a higher response to the β-adrenergic agonist. These responses were blocked by the H-nclreiicrBie antagonist propranolol (10/im). The β-adrenergic response increased rapidly with culture time. The addition of cycloheximide (5/*m) to the culture abolished the expression of adrenergic response. The enhanced β-adrenergic response by 20ng/ml EGF was partially inhibited hy the addition of cytochalasin B (20/iM) to the culture. The cAMP-producing response to metaproterenol (10 /im) was dose-dependently inhibited by the specific a2-afionist UK-14304. Pretreatment of the hepatocytes with pertussis toxin (lOOng/ml) potentiated the β-adrenergic response. These results demonstrate that augmented β-adrenergic responsiveness can be acquired by adult rat hepatoeytes cultured with 20ng/ml EGF at a low cell density, and the ^-adrenergic response involves tk now synthesis of protein(s). The results also show that significant a2- and /J-adrenergic responses coexist in the primary cultures of adult rat hepatocytes.