Phosphorylated β-guanidinopropionate as a Substitute for Phosphocreatine in Rat Muscle
Format of Original
American Physiological Society
American Journal of Physiology
To evaluate phosphorylated β-guanidinopropionate (β-GPAP) as a substitute for phosphocreatine (PC), hypoxic tibialis anterior muscles were stimulated to contract isometrically in situ until twitch tension fell to 25% of the peak value. Muscles from rats fed β-guanidinopropionic acid (β-GPA) failed to exhibit the staircase phenomenon, and they developed 28% less tension than control muscles. In control muscles lactate increased from 0.75 to 20.99, ADP increased from 0.89 to 1.20, ATP decreased from 5.09 to 2.73, and PC decreased from 15.78 to 1.52 μmol/g. In muscles from rats fed β-GPA, lactate increased from 0.85 to 14.31, ADP increased from 0.86 to 1.06, ATP decreased from 2.69 to 1.71, PC decreased from 0.73 to 0.30, and β-GPAP decreased from 30.34 to 19.45 μmol/g. From these measurements, the use of high-energy phosphate was calculated to be reduced 32% in muscles from rats fed β-GPA. The relationships between the use of high-energy phosphate and tension development confirm experimentally the ability of β-GPAP to substitute for PC as a source of energy to sustain muscle contraction.