METABOLITE UTILIZATION AND COMPARTMENTATION IN PORCINE CAROTID-ARTERY - A STUDY USING BETA-GUANIDINOPROPIONIC ACID

The relationship between substrate and metabolism in vascular smooth muscle has been investigated by studying the acute energetic effects caused by the creatine analogue beta-guanidinopropionic acid (beta-GPA) on porcine carotid arteries using P-31-nuclear magnetic resonance (NMR). Porcine carotid arteries were superfused for 12 h with Krebs-Henseleit buffer at 22 degrees C, containing 50 mM beta-GPA, and either 11 mM glucose or 5 mM pyruvate as substrate. beta-GPA enters the cells and becomes phosphorylated by creatine kinase to produce beta-GPA-P. Perfusion with beta-GPA leads to the formation of NMR observable beta-GPA-P (after 2.5 h). The appearance of beta-GPA-P with time was significantly greater when glucose was used as substrate. To differentiate between oxidative and glycolytic metabolism in the phosphorylation of beta-GPA, 1 mM cyanide was included in the perfusion buffer containing 50 mM beta-GPA and 11 mM glucose. No phosphocreatine (PCr) was observed with these conditions, and there was a small but significant decrease in ATP concentration ([ATP]) compared with glucose perfusion without cyanide (0.56 +/- 0.02 to 0.47 +/- 0.02 mu mol/g wet wt), that was greater than the concentration with pyruvate as substrate (0.25 +/- 0.03 mu mol/g wet wt). Thus the [ATP] during cyanide treatment is maintained with glycolytic metabolism. Despite the relatively high [ATP], accumulation of beta-GPA-P only occurred over a much slower time course (>10 h) than without cyanide. We conclude that the rate of beta-GPA-P accumulation is substrate dependent and that the relatively high [ATP] with no observable PCr or beta-GPA phosphorylation with cyanide supports an energetic compartmentation in the porcine carotid artery.