Effects of tetrodotoxin-induced neural inactivation on single muscle fiber metabolic enzymes.
Selected enzymes were measured in mixed-fiber bundles and individual fibers from rat plantaris (PL) and soleus (Sol) muscles that had undergone either 2 wk of tetrodotoxin (TTX) inactivation of the sciatic nerve, a sham operation, or were contralateral to the TTX limb. TTX disuse caused severe wasting of PL (46%) and Sol (26%) muscles and of single fibers (50% and 40%, respectively). TTX PL and Sol also had reduced (50%) glycogen content. In TTX, PL, and Sol macro samples and single fibers, the activities (mol.h-1.kg dry wt-1) of hexokinase, glycogen phosphorylase, and lactate dehydrogenase were higher, lower, and unchanged, respectively, compared with controls. Single-fiber data showed that these changes occurred in all fibers. In TTX PL macro samples, activities of glycerol-3-phosphate dehydrogenase (GPDH), pyruvate kinase (PK), malate dehydrogenase (MDH), citrate synthase (CS), beta-hydroxyacyl-CoA dehydrogenase (BOAC), and thiolase were, or tended to be, lower. Single-fiber data showed a disappearance of high-oxidative moderate glycolytic fibers (i.e., usually fast-twitch oxidative in control) and the appearance of more fibers with a metabolic enzyme profile approaching that of control slow-oxidative fibers. In TTX Sol macro samples, GPDH and PK tended to be higher, and thiolase, BOAC, CS, and MDH lower. Single-fiber data corroborated these findings and suggested the appearance of fast fibers with downregulated oxidative enzyme profiles. Our results suggest that neuromuscular activity is a major, but not the sole, determinant of the size and metabolic heterogeneity that exists in muscle cells.
Michel
R N
RN
School of Human Movement, Laurentian University, Sudbury, Ontario, Canada.
Cowper
G
G
Chi
M M
MM
Manchester
J K
JK
Falter
H
H
Lowry
O H
OH
D000818:Animals; D005260:Female; D006614:Hindlimb; D009132:Muscles / Q000201:enzymology* / Q000294:innervation*; D010243:Paralysis / Q000139:chemically induced* / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000187:drug effects* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology*
D013779:Tetrodotoxin