Proton magnetic resonance spectroscopy (1H-MRS) is a technique that can differentiate lipids stored within adipocytes (extramyocellular lipid, EMCL) from intramyocellular lipid (IMCL) stored as droplets on the CH5424802 mouse border of the myoplasm [122–127]. This differentiation is based on the variance in resonance frequency between protons contained in relatively cylindrical KU55933 order deposits of EMCL in adipocytes and protons contained in IMCL deposits which are spherical in shape. These resonances show up as different peaks on the proton spectrum of skeletal muscle (Fig. 5). Probing IMCL is of clinical importance because IMCL stores represent lipid which borders mitochondria and which represent
an energy supply of free fatty acids for oxidation. IMCL intensity determined by 1H-MRS has been found to correlate with insulin resistance and obesity. The risk of insulin resistance is known to increase with
age, and aging skeletal muscle is characterized MMP inhibitor by decreasing oxidative capacity that may lead to increased IMCL. Fig. 5 MRI image of calf at the right, with green and yellow boxes indicating locations of spectroscopic acquisitions of the tibialis anterior and soleus muscles, respectively. Proton spectroscopy studies may be used to assess the relative amounts of intramyocellular and extramyocellular lipid. At the right, a proton spectrum corresponding to the soleus muscle shows 1H resonances associated Calpain with creatinine (CR2 and CR3), water, extramyocellular lipid (EMCL), intramyocellular lipid (IMCL), and trimethylamines (TMA) MRS may also be used to detect resonances
of 31P and 13C nuclei contained in ATP, ADP inorganic phosphate, glycogen, and other chemical forms in skeletal muscle cells, shedding important light on muscle metabolism. 31P-MRS can be used to directly analyze relative abundances of 31P contained in compounds of interest to energetics of skeletal muscle, including ATP, inorganic phosphate, and phosphocreatine [128–134]. Based on these primary measurements, it is also possible to use 31P-MRS to indirectly estimate the intracellular pH, as well as the free concentrations of ADP and Mg2+ ions. These measurements allow the technique to be used to estimate rates of ATP synthesis under ischemic (glycogenolytic) conditions or aerobic (oxidative) conditions. Other applications in skeletal muscle studies include estimates of the oxidative capacity of skeletal muscle, as well as the proton efflux and buffer capacity, which provide insight into the recovery of skeletal muscle from exercise. The wide chemical shift of the 13C resonance allows 13C-MRS to assess the relative abundances of a wide range of molecules related to glycogen synthesis and glycogenolysis [129, 135–143]. Using the natural abundance (1.1%) of 13C, it is possible to detect resonances of 13C in glycogen and triglyceride.