Regulation of Glycogen Utilization, but Not Glucose Utilization, by Precontraction Glycogen Levels in Vascular Smooth Muscle

Abstract

These experiments were designed to determine whether glycogenolysis was influenced by the glycogen concentration of vascular smooth muscle. Segments of hog carotid artery smooth muscle were allowed to synthesize variable amounts of 1-[13C]glucosyl units of glycogen. Artery segments were then isometrically contracted in the presence of 2-[13C]glucose. Prior to and after isometric contraction, measurements were made of tissue glycogen content and superfusate glucose and lactate concentrations. 2-[13C]Lactate and 3-[13C]lactate peak intensities in the superfusate were measured using 13C-NMR spectroscopy. The tissue glycogen content decreased exponentially during the 4.5 h of isometric contraction (R2 = 0.990), despite more than a 3-fold range of glycogen concentration prior to contraction. The extent of glycogen utilization during a 3 h isometric contraction varied linearly with the precontraction glycogen concentration (R2 = 0.727). Lactate production specifically from glycogen breakdown increased with an increase in precontraction glycogen concentration (R2 = 0.620). During a 3 h isometric contraction neither the glucose utilization (R2 = 0.007) nor lactate production specifically produced from glucose (R2 = 0.00002) varied with the precontraction glycogen concentration. It is concluded that the rate of glycogenolysis is determined by the content of glycogen during prolonged contractions. In addition, precontraction glycogen levels influence the pathway for glycogen utilization but not the pathway for glucose utilization. Therefore, glycolysis and glycogenolysis behave independently in vascular smooth muscle.

Sorting of metabolic pathway flux by the plasma membrane in cerebrovascular smooth muscle cells

“…Thus each intermediate remains within the pathway, making it unavailable for use by other pathways in which it is also an intermediate (compartmentation). Compartmentation of glycolytic, gluconeogenic, and glycogenolytic intermediates has been shown in previous studies in our laboratory (9,(11)(12)(13) and others (1,15).…”

“…A 650-µl aliquot of this solution was transferred to a 5-mm NMR tube for NMR spectroscopy. 13 C-NMR was performed using a Bruker DRX 500 spectrometer. One thousand two hundred scans were acquired after sixty-four dummy scans using a 30°pulse angle at 125.77 MHz, 33,333-Hz sweep width, and 1-s predelay.…”

“…We have recently found that vascular smooth muscle of isolated pig cerebral microvessels (PCMV) utilizes [1- 13 13 C]FBP derived from glucose breakdown, and this tissue exhibits a compartmentation of glycolysis and gluconeogenesis (18). Because glycolytic enzymes are known to associate with microtubules, we examined the role of microtubules in compartmentation of glycolysis and gluconeogenesis.…”

Key Role of Glycogen Storage in High K⁺-Induced Contraction of the Smooth Muscles of the Bovine Trachea

“…These results also suggest that the production of ATP for maintaining muscle contraction in vascular smooth muscles is similar to that in the bovine trachea. However, some researchers have shown that the tissue glycogen content was decreased with high K + -induced contraction in the guinea pig taenia coli [19] and porcine carotid artery [11] under aerobic conditions. More studies should be conducted to investigate the compartmentalization of the pathways of exogenous glucose and endogenous glycogen utilization for maintaining muscle contraction in smooth muscles under energy-limited conditions.…”

“…On the other hand, some researchers have shown that glucose-free PSS or hypoxia have little effects on contraction of vascular smooth muscle, such as the aorta and carotid artery [20,23], and it has been reported that endogenous glycogen storage is used to maintain muscle contraction in the carotid artery [11,20]. However, the relationship between endogenous glycogen storage and the ability to main-tain contraction in tonic smooth muscles (such as vascular smooth muscle) in an energy limiting condition is not well known.…”