EFFECTS OF BETA-GUANIDINOPROPIONIC ACID-FEEDING ON THE PATTERNS OF MYOSIN ISOFORMS IN RAT FAST-TWITCH MUSCLE

Administration of beta-guanidinopropionic acid (beta-GPA) to rats as 1 % of their diet for 6 weeks led to an accumulation of beta-GPA and bet a-GPA-phosphate and to a depletion of creatine and phosphocreatine in the fast-twitch plantaris muscle. Adenosine triphosphate concentration was also decreased. Electrophoretic analyses were performed to invest igate the effects of beta-GPA on the patterns of fast (FM) and slow (S M) isomyosins, myosin heavy chain (HC) isoforms and myosin light chain (LC) isoforms. The relative concentrations of fast isomyosins FM1 and FM2 decreased, whereas slow isomyosin SM increased. The increase in s low isomyosin corresponded to an increase in the relative concentratio n of the slow myosin HCI. The changes of the myosin light chain patter n consisted of increases in the relative concentrations of the two slo w isoforms, LC1sb and LC2s, and decreases in the fast isoforms LC2f an d LC3f. These results demonstrate that beta-GPA administration, leadin g to a depletion in energy-rich phosphates and a reduced phosphorylati on potential, has an impact on myosin isoform expression in rat fast-t witch skeletal muscle.