Dynamic changes in intact crystalline lens metabolism modulated by alkaline earth metals: I. Effects of magnesium

Dynamic changes in organophosphate levels during incubation of the intact crystalline lens in Earle's buffer containing 10 and 20 mM-MgCl2 were studied using phosphorus-31 nuclear magnetic resonance spectroscopy. Twenty-eight phosphatic metabolites of intermediary metabolism were quantitated and the utilization of these compounds was determined during a 24-hr time-course. In addition, intralenticular pH was assessed from both the resonance position of alpha-glycerophosphate and inorganic orthophosphate as measured in the intact tissue. Generally, high extracellular magnesium concentrations promote a net reduction of ATP with a concomitant production of inorganic orthophosphate; however, subtle changes occur in the metabolic processes which modulate this primary activity. The most notable difference between incubation in 10 and 20 mM-magnesium is that during 20 mM-magnesium incubations the intralenticular pH decline is proportionate to the net ATP consumption; however, in response to 10 mM-magnesium, the intralenticular pH becomes alkalotic in conjunction with the decrease in intralenticular ATP levels. The demonstration that high extracellular magnesium concentrations significantly alter lens metabolite levels is presumptive evidence that lens metabolic activity may be modulated through cellular mechanisms involving magnesium-sensitive processes.