Inhibition of glycogenolysis in primary rat hepatocytes by 1,4-dideoxy-1,4-imino-d-arabinitol

1,4-Dideoxy-1,4-imino-D-arabinitol (DAB) was identified previously-as a pot ent inhibitor of both the phosphorylated and non-phosphorylated forms of gl ycogen phosphorylase (EC 2.4.1.1). In the present study, the effects of DAB were investigated in primary cultured rat hepatocytes. The transport of DA B into hepatocytes was dependent on time and DAB concentration. The rate of DAB transport was 192 pmol/min per mg of protein per mM DAB(medium-concent ration). In hepatocytes, DAB inhibited basal and glucagon-stimulated glycog enolysis with IC50 values of 1.0 +/- 0.3 and 1.1 +/- 0.2 mu M, respectively . The primary inhibitory effect of DAB on glycogenolysis was shown to be du e to inhibition of glycogen phosphorylase but, at higher concentrations of DAB, inhibition of the debranching enzyme (4-alpha-glucanotransferase, EC 2 .4.1.25) may have an effect. No effects on glycogen synthesis were observed , demonstrating that glycogen recycling does not occur in cultured hepatocy tes under the conditions tested. Furthermore, DAB had no effects on phospho rylase kinase, the enzyme responsible for phosphorylation and thereby activ ation of glycogen phosphorylase, or on protein phosphatase 1, the enzyme re sponsible for inactivation of glycogen phosphorylase through dephosphorylat ion.