Effects of carbamylcholine and pyridostigmine on cytoskeleton-bound and cytosolic phosphofructokinase and ATP levels in different rat tissues.

1. The effects of carbamylcholine (CaCh) (acetylcholine agonist) and pyridostigmine (Pyr) (acetylcholinesterase inhibitor), on the activity of cytoskeleton-bound and cytosolic phosphofructokinase (PFK), the rate-limiting enzyme in glycolysis, and ATP levels, were studied in rat tibialis anterior (TA) muscle, heart, and brain. 2. In the TA muscle, a marked (about three-fold) increase in the allosteric activity of cytosolic (soluble) PFK was found, 3-5 min following the injection of CaCh or Pyr. The intracellular distribution of the enzyme was not affected by both drugs. Stimulation of glycolysis in this muscle was also expressed by a significant increase in the concentrations of glycolytic intermediates and lactate. Glucose 1,6-bisphosphate (Glc-1,6-P2) levels were unchanged, whereas fructose-2,6-bisphosphate (Fru-2,6-P2) was increased. Glycogenolysis was also stimulated, as deduced from the decrease in glycogen content. The stimulation of glycolysis, induced by both drugs, was accompanied by an increase in ATP level in the TA muscle. 3. In contrast to the stimulatory action of CaCh or Pyr on glycolysis in the TA muscle, both drugs had no effect on cytosolic and cytoskeletal PFK in heart and brain. However, ATP content in both heart and brain was markedly reduced by these drugs, most probably due to their reported harmful effects on mitochondrial function, leading to tissue damage. 4. Electron microscopic studies of TA muscle and heart from rats treated with CaCh or Pyr, revealed severe damage of heart but no harmful effects on TA muscle, which is a muscle with high glycolytic and low oxidative capacity. The present experiments suggest that the accelerated glycolysis in this muscle induced by both drugs, supplies ATP, thus preventing muscle damage.