Intraneuronal [Ca2+] changes induced by 2-deoxy-D-glucose in rat hippocampal slices

Temporary replacement of glucose by 2-deoxyglucose (2-DG; but not sucrose) is followed by long-term potentiation of CA1 synaptic transmission (2-DG LT P), which is Ca2+-dependent and is prevented by dantrolene or N-methyl-D-as partate (NMDA) antagonists. To clarify the mechanism of action of 2-DG, we monitored [Ca2+](i) while replacing glucose with 2-DG or sucrose. In slices (from Wistar rats) kept submerged at 30 degrees C, pyramidal neurons were loaded with [Ca2+]sensitive fluo-3 or Fura Red. The fluorescence was measur ed with a confocal microscope. Bath applications of 10 mM 2-DG (replacing g lucose for 15 +/- 0.38 min, means +/- SE) led to a rapid but reversible ris e in fluo-3 fluorescence (or drop of Fura Red fluorescence); the peak incre ase of fluo-3 fluorescence (Delta F/F-0), measured near the end of 2-DG app lications, was by 245 +/- 50% (n = 32). Isosmolar sucrose (for 15-40 min) h ad a smaller but significant effect (Delta F/F-0 = 94 +/- 14%, n = 10). The 2-DG-induced Delta F/F-0 was greatly reduced (to 35 +/- 15%, n = 16) by D, L-aminophosphono-valerate (50-100 mu M) and abolished by 10 mu M dantrolene (-4.0 +/- 2.9%, n = 11). A substantial, although smaller effect, of 2-DG p ersisted in Ca2+-free 1 mM ethylene glycol-bis(beta-amino-ethyl ether)-N,N, N',N'-tetraacetic acid (EGTA) medium. Two adenosine antagonists, which do n ot prevent 2-DG LTP, were also tested; 2-DG-induced Delta F/F-0 (fluo-3) wa s not affected by the A(1) antagonist 8-cyclopentyl-3,7-dihydro-1,3-dipropy l-1H-purine-2,6-dione (DPCPX 50 nM; 287 +/- 38%; n = 20), but it was abolis hed by the A(1)/A(2) antagonist 8-SPT; 25 +/- 29%, n = 19). These observati ons suggest that 2-DG releases glutamate and adenosine and that the rise in [Ca2+] may be triggered by a synergistic action of glutamate (acting via N MDA receptors) and adenosine (acting via A(2b) receptors) resulting in Ca2 release from a dantrolene-sensitive store. The discrepant effects of sucro se and X-SPT on Delta F/F-0, on the one hand, and 2-DG LTP, on the other, s upport other evidence that increases in postaynaptic [Ca2+](i) are not esse ntial for 2-DG LTP.