Manganese as a calcium probe: Electron paramagnetic resonance and nuclear magnetic resonance spectroscopy of intact cells

Abstract

When Lettree cells are exposed to Mn²⁺, the cation becomes associated with cells in two ways: in a relatively loose and mobile manner that gives a six-line EPR spectrum designated Mn _b ^*, and in an immobile, relatively tight manner that gives no detectable EPR spectrum, designated Mn _b . Mn _b ^* is probably on the surface of cells; most Mn _b is probably inside cells. NMR measurements of Lettree cell suspensions show two water proton relaxation rates and confirm the existence of cell-associated Mn. Human erythrocytes, on the other hand, bind no Mn²⁺ under these conditions, as judged by EPR and NMR measurements. Virally-treated Lettree cells show an increase in Mn _b (but not in Mn _b ^*). They also show a third water proton relaxation rate.