27Mg2+ and 28Mg2+ : preparation and use as radiotracers in magnesium physiology orientated studies of tilapia

In spite of the pivotal role of magnesium in many life processes, insight into its physiology is still limited. This is partially due to the scarcity and the short half-lives of magnesium radioisotopes to be used as radiotracers for magnesium. Among the radioisotopes of magnesium only two are suitable for physiological studies, namely 27Mg (t1/2 = 9.46 minutes) and 28Mg (t1/2 = 20.92 hours). Both were obtained by thermal neutron irradiation of magnesium-containing material in the IRI nuclear reactor, which was, in the case of 28Mg, followed by radiochemical separation. The final specific activities of 27Mg and 28Mg preparations were about 50 and 0.25-1 GBq.mol-1, respectively. 27Mg2+ and 28Mg2+ were used as radiotracers for Mg2+ in studies of magnesim uptake by basolateral plasma membrane inside-out orientated vesicles of tilapia (freshwater fish) enterocytes and its transport to fish from water. The experiments led to the following results: the rate of ATP-dependent magnesium uptake by the vesicles was about 0.02 nmol.s-1 per mg protein and the magnesium intake or the "flow to fish from water" Ffw nmol.h -1 depends on tilapia weight Wfg conform to the relation Ff = 4.65 (Wf)'0.58. The experiments showed that the half-lives and the activities as well as the specific activities ofboth radioisotopes were adequate to obtain the information required.