Smooth muscle and NMR review: an overview of smooth muscle metabolism.

Nuclear magnetic resonance (NMR) is a non-invasive technique which allows us to examine the biochemical, physiological and metabolic events occurring inside living tissue; such as vascular and other smooth muscles. It has been found that the smooth muscle metabolism is compartmented such that mitochondrial function fuels contraction and that much glycolytic ATP production is used for membrane pumps. Using NMR we have been able to observe the ATP and phosphocreatine (PCr) concentrations and estimate the ADP concentration, as well as flux through the creatine kinase (CK) system. It has also been found that the smooth muscle metabolism is able to maintain ATP concentration in the absence of mitochondrial function (cyanide inhibition). Therefore, the vessels are able to adapt to metabolic demands as necessary. NMR is versatile in the information it can provide because it has also yielded important contributions with regard to the intracellular pH and ionic status. For example, the intracellular free Mg2+ ([Mg2+]i) can be measured with NMR simultaneously with ATP concentrations and NMR has shown us that the [Mg2+]i is highly protected in the muscle (within confined range), but also responds to the environment around it. In this review we conclude that NMR measurements of smooth muscle research is a useful technique for assessing chronic and acute changes that occur in the tissue and during diseases.