Cytosolic & Lysosomal Glycogen Metabolism

It is now well established that the metabolism of glycogen in the l iver p roceeds h y d r o l y t i c a l l y through the lysosomal compar tment (Geddes & Taylor, 1985; Geddes et al .~ 1983; Geddes & Stratton~ 1977a,b; LCillman-Rauch 1981, 1982; Knecht & Hernandez, 1978; Brown et al., 1978; Rybicka, 1981) as well as through the well-established s y n t h e t i c phospho ry ly t i c pathways (Cohen, 1982). The glycogens isolated from lysosomal preparations appear to be structurally different f rom c y t o s o l i c g lycogens (Calder & Geddes, 1983; 1985; Chee & Geddes, 1977) but, in addition, are easily distinguishable by their large molecular size (Geddes, 1971; Geddes & Stratton 1977; Geddes et al., 1977a,b; Geddes et al., 1983; Geddes & Taylor, 1995; Geddes, 1985). The well established 'metabolic inhomogeneity' of glycogen (Stet ten & Stetten, 1954, 1955) is clearly related to this compartmentat ion of the separate degradation mechanisms and the isolation of the synthetic pathway in the cytosol (Geddes & Stratton 1977a,b; Geddes et al., 1983; Geddes & Taylor 1985; Ching et al., 1985). Use of a rat strain (NZR/Mh) lacking phosphorylase kinase had enabled some metabolic s tud ies of the e f fec t of enzymic disturbance within the cytosolic compartment and its relationship to hormonal control to be undertaken (Malthus & Clark, 1977; Malthus et al., 1980; Gain et al., 19gl; Clark et al., 1982). Recently studies with Acarbose, a 1,/~-e-glucosidase i n h i b i t o r , h a v e shown tha t lysosomal g lycogenos i s is induced (L( i l lman-Rauch 1981, 1982) and that the overall metabolism of glycogen in the cell is a f fec ted (Geddes & Taylor, 1985). This paper examines the e f f ec t of Acarbose on hepatic glycogen metabolism in the phosphorylase kinase deficient rats.