INFLUENCE OF HYPERGLYCEMIA AND OF HYPERCAPNIA ON CELLULAR CALCIUM TRANSIENTS DURING REVERSIBLE BRAIN ISCHEMIA

The object of the study was to find out how preischemic hyperglycemia (in normocapnic animals) or excessive hypercapnia (in normoglycemic an imals) affect the calcium transient during ischemia, as this can be as sessed by measurements of the extracellular calcium concentration ([Ca 2+](e)). To that extent, normocapnic-normoglycemic control animals wer e compared with animals with induced hyperglycemia or hypercapnia, all being subjected to 10 min of forebrain ischemia, the [Ca2+](e) and d. c. potential being measured with ion-sensitive glass microelectrodes. Hyperglycemia and hypercapnia delayed the loss of ion homeostasis foll owing induction of ischemia. Furthermore, both hyperglycemia and hyper capnia reduced the delay of Ca2+ extrusion upon recirculation. As a re sult, both hyperglycemia and hypercapnia significantly reduced the isc hemic calcium transient, as this was assessed by calculating the durat ion of maximal calcium load of cells. The results make it less likely that aggravation of brain damage by hyperglycemia or excessive hyperca pnia is related to a further derangement of cell calcium homeostasis.