Differential change of Ins-P 3-Ca 2+ signaling during culture of rat hepatocytes

Abstract

Decrease of α-adrenergic responses during primary culture of rat hepatocytes was studied. Activation of glycogen phosphorylase by phenylephrine was decreased in the early stage of the culture (within 6 h), however, Ins-P 3 production was almost intact until 12 h of the culture and then declined. α-Adrenoceptor-mediated Ca 2+-mobilization and Ins-P 3-induced Ca 2+ release from microsomal fractions were decreased in the early stage of the culture, similar to the above change of phosphorylase activation. We found that decrease of Ins-P 3-binding sites in the early stage of the culture was the cause of differential change of Ins-P 3-Ca 2+ signaling during the culture of hepatocytes. Similar changes described above were also observed in vasopressin-induced responses. However, the changes of Ins-P 3-Ca 2+ signaling did not occur in a high-cell density culture of rat hepatocytes. In conclusion, the loss of phenylephrine- and vasopressin-induced responses in cultured liver cells appear to be due to change of Ins-P 3-binding sites as well as decreased Ins-P 3 production due to reduction of receptor numbers.