The dominant RN- gene affects meat quality of pigs by increasing the glycogen content of muscle. Glycogen localization was studied in Longissimus dorsi muscle from RN- carrier pigs (RN- pigs) and rn+ rn+ homozygous pigs (rn+ pigs). 2. Ultrastructural study showed an excess of glycogen in the sarcoplasm of white fibres from RN- pigs as compared to rn+ pigs. 3. Lysosome-enriched fractions extracted from muscles contained 6% of the tissue glycogen content in both types of pigs. The distribution of the glycogen particles between sarcoplasm and lysosomes appeared to be similar in both RN- and rn+ pig tissues. 4. White fibres from RN- pigs with an increased glycogen level showed two ultrastructural alterations: the sarcoplasmic compartment was abnormally enlarged and a large proportion of mitochondria was morphologically modified. 5. The RN- gene seems, therefore, to be associated with alterations in the glycolytic metabolism, in the distribution of proteic compartments and in the oxidative metabolism of white muscle fibres.
