Evaluation of 26Mg stable isotope as an in vivo tracer of magnesium transport for SIMS ion microscopy imaging studies.

Abstract

Isotopic detection with high sensitivity, one of the most important features of ion microscopy, allows the in vivo application of stable isotopes 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 necessity for tracer studies with stable isotopes. We have tested the feasibility of 26Mg stable isotope as a tracer of magnesium transport in the killifish. The fish were given a single intraperitoneal injection of 3 mumol 26MgCl2.6H2O (99.5% 26Mg enrichment), and the renal distribution of 26Mg was examined in frozen freeze-dried cryosections with ion microscopy. High-mass resolution analyses were performed to evaluate the purity of positive secondary ion signals of the nominal masses 24, 25 and 26 in order to assess the purity of 24Mg, 25Mg and 26Mg signals, respectively, in kidneys of control and 26Mg-injected fish. In kidneys of control fish, the purities of 24Mg, 25Mg and 26Mg signals were approximately 97%, 82% and 90%, respectively. In fish that were injected with 26Mg stable isotope, an enhancement of 26Mg+ secondary ion signals was observed with signal purity reaching 95%. These observations indicate that 26Mg can be used successfully as a tracer of magnesium transport in animal models. To uncover the distribution of tracer 26Mg from the naturally abundant background of this isotope, a pixel-by-pixel digital subtraction is applied to the raw ion microscopy mass 26 image.