NMR analysis of transporting epithelia.

Three specific examples have been discussed, illustrating how NMR spectroscopy has, is, and will be providing useful complementary information in the study of transepithelial sodium transport. In a brief introduction to principles of NMR, the concepts have first been presented of: nuclear magnetic energy levels, dipolar and quadrupolar interactions, bulk magnetization, Larmor frequency, chemical shift, relative integrated area, longitudinal and transverse relaxations, line width, correlation time, immobilization, compartmentalization, and nuclear exchange. In the three succeeding sections of the review, examples have been provided of how NMR can be used to quantify the degree of intracellular binding of Na+ and K+, relate measurements of the intracellular phosphates to studies of transepithelial Na+ transport, and monitor the content of intracellular Na+. Emphasis has been placed on the value of NMR spectroscopy as a non-invasive probe of nuclides of biological interest. However, note has also been made of the limited sensitivity of the technique and the complexity in analysis posed by cellular and subcellular compartmentalization. Some of these complexities are now being addressed by spin transfer NMR techniques.