Biological Imaging and Spectroscopy of pH

Valery   V.   Khramtsov

doi:10.2174/1385272054038309

Abstract

The critical role of pH status in physiology and pathophysiology of living organisms is well recognized. This includes local acidosis induced by ischemia, infection or inflammation, extracellular acidosis in tumors, depth-specific tissue pH variations during skin treatments or wound healing, etc. At the microscopic scale local pH drastically affects the vital activities of cell, cellular organelles and enzymes. Upon therapeutic intervention, the delivery, absorption and pharmacological effectiveness of drugs can be altered by changing the pH of their local environment. Therefore, spatially and temporarily addressed pH measurements in vivo are of considerable clinical relevance. At subcellular levels, spatiotemporal pH assessment provides significant insight into the mechanisms of pH regulation in cellular organelles and its role in cellular signaling including cell proliferation and apoptosis. Current methods in biological pH detection and imaging, their limits, advantages and recent applications, as well as further perspectives of their development are discussed. Non-invasive spectroscopic approaches mostly rely on endogenous or/and exogenous molecular probes that are weak acids or bases with pH-dependable spectral properties. Absorption and fluorescent probes may be considered particularly effective for pH studies on cellular and subcellular levels, while magnetic resonance approaches based on EPR and NMR spectroscopies have the advantage for in vivo applications in animals and humans. Special emphasis is given to EPR spectroscopy due to the rapid development of lowfield EPR techniques and new pH sensitive probes with enhanced spectral properties making in vivo pH detection and imaging possible.

Keywords: intracellular compartments, homeostasis, ph-imaging, molecular ph probes, fluorescence, nmr spectroscopy, mapping, epr spectroscopy