EVALUATION OF MG-26 STABLE-ISOTOPE AS AN IN-VIVO TRACER OF MAGNESIUM TRANSPORT FOR SIMS ION MICROSCOPY IMAGING STUDIES

Isotopic detection with high sensitivity, one of the most important fe atures of ion microscopy, allows the in vivo application of stable iso topes as tracers for unravelling smaller tissue structures implicated with transport capabilities. The evaluation of the mass interferences associated with a particular mass of secondary ion signals is a necess ity for tracer studies with stable isotopes. We have tested the feasib ility of Mg-26 Stable isotope as a tracer of magnesium transport in th e killfish. The fish were given a single intraperitoneal injection of 3 mu mol (MgCl2)-Mg-26 . 6H(2)O (99.5% Mg-26 enrichment), and the rena l distribution of Mg-26 was examined in frozen freeze-dried cryosectio ns with ion microscopy. High-mass resolution analyses were performed t o evaluate the purity of positive secondary ion signals of the nominal masses 24, 25 and 26 in order to assess the purity of Mg-24, Mg-25 an d Mg-26 signals, respectively, in kidneys of control and Mg-26-injecte d fish. In kidneys of control fish, the purities of Mg-24, Mg-25 and M g-26 signals were approximate to 97%, 82% and 90%, respectively. In fi sh that were injected with Mg-26 stable isotope, an enhancement of Mg- 26(+) secondary ion signals was observed with signal purity reaching 9 5%. These observations indicate that Mg-26 can be used successfully as a tracer of magnesium transport in animal models. To uncover the dist ribution of tracer Mg-26 from the naturally abundant background of thi s isotope, a pixel-by-pixel digital subtraction is applied to the raw ion microscopy mass 26 image.