Studies on responsiveness of hepatoma cells to catecholamines. II. Comparison of .BETA.-adrenergic responsiveness of rat ascites hepatoma cells with cultured normal rat liver cells.

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The pharmacological properties of β-adrenoceptors in rat ascites hepatoma cells were compared with those in normal rat liver cells which were cultured for 24 hr after collagenase digestion. Adenylate cyclases in the homogenates of cultured normal rat liver cells and rat ascites hepatoma cells, AH44, AH66, AH109A, AH130 and AH7974, were all activated by isoproterenol or NaF to different degrees. The enzyme in rat liver cells was activated by several β2-agonists but those in all hepatoma cells hardly responded. Furthermore, salbutamol, a β2-partial agonist, antagonized the cyclase activation by isoproterenol in AH130 cells. The Kact value of isoproterenol for the activation of adenylate cyclase in AH1 30 cells was smaller than that in rat liver cells. A comparison of the Ki values of β-antagonists for the inhibition of isoproterenol-stimulated cyclase activity shows that while the Ki values of propranolol and butoxamine in AH130 cells were similar to those in rat liver cells, a significant difference was observed in the values for β1-selective antagonists between AH130 cells and rat liver cells. The Ki values of metoprolol and atenolol for AH130 cells were 137- and 90-fold lower, respectively, than for normal rat liver cells. From these findings, it is strongly suggested that β-adrenoceptors in rat ascites hepatoma cells including AH130 cells have similar properties to the mammalian β1-receptor.
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