INTERNAL CA2-NEURONS( STORES INVOLVED IN ANOXIC RESPONSES OF RAT HIPPOCAMPAL)

1. During whole-cell recordings from CA1 neurons of rat brain slices w ith electrodes containing only KMeSO(4) and Hepes, brief anoxia (2-3 m in) consistently evoked a hyperpolarization (Delta V approximate to -4 mV) and reduction in input resistance (Delta R approximate to -20%). 2. As in previous intracellular recordings, Dantrolene sodium (10 mu M ) suppressed the anoxic Delta V and Delta R, confirming that the relea se of internal Ca2+ is a major component of the anoxic response. 3. To identify the relevant intracellular Ca2+ store, other blockers of Ca2 + release were applied either externally (in the bath) or internally, by addition to the contents of the recording electrode. 4. The anoxic hyperpolarization was abolished or much reduced by heparin (10-20 mu g ml(-1) internal), thapsigargin (10 mu M, external), Ruthenium Red (50 mu M, internal) and external procaine (0.5-2 mu M), but not by intern al procaine (0.5-1 mM) or ryanodine (10 mu M, external). 5. The anoxic fall in resistance was also abolished or reduced by heparin, thapsiga rgin and external procaine, but not by ryanodine, internal procaine or Ruthenium Red. 6. In addition, external procaine (0.5-2 mM) eliminate d the early (transient) depolarization and reduced the post-anoxic hyp erpolarization by 60 +/- 22%. 7. None of these agents consistently cha nged the resting potential, but the input resistance was significantly increased by Dantrolene and external procaine. 8. In view of the mark ed effects of heparin and thapsigargin, but not ryanodine and internal procaine, we conclude that the anoxic response seen in such whole-cel l recordings is initiated predominantly by Ca2+ release from an intern al store that is InsP(3) sensitive rather than Ca2+ sensitive. 9. Comp arable but less pronounced effects of external procaine were seen duri ng intracellular recordings with 3 M KCl-containing electrodes. The do se-dependent suppression of various features of the anoxic response by external procaine (EC(50) approximate to 0.2 mM) is presumed to be me diated by a superficial membrane trigger or modulating site.