Pharmacological manipulations of ATP-dependent potassium channels and adenosine A1 receptors do not impact hippocampal ischemic preconditioning in vivo: evidence in a highly quantitative gerbil model.

Ischemic preconditioning models have been characterized in brain, heart, and other tissues, and previous pharmacologic studies have suggested an involvement of adenosine and ATP dependent potassium (KATP) channels in such tolerance phenomena. This question was reexamined in a reproducible gerbil model in which the duration of ischemic depolarization defined the severity of preconditioning and test insults. Agents studied were glibenclamide, a blocker of KATP channels; 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), an adenosine A1 receptor antagonist; and N6-cyclopentyladenosine (CPA), an A1 agonist. Intraventricular glibenclamide injections aggravated neuron damage after brief priming insults, in parallel with a dose-dependent prolongation of ischemic depolarization. However, the depolarization thresholds for ischemic neuronal injury were identical in vehicle- and glibenclamide-treated animals, and glibenclamide did not affect preconditioning when equivalent insult severity was maintained during priming insults. Neither DPCPX nor CPA had any effect on the onset or duration of depolarization after intraperitoneal injection in this model, and neither drug affected neuron damage. In the case of CPA, it was necessary to maintain temperature for 4 to 6 hours of recirculation to avoid significant confounding hypothermia. These results fail to support a direct involvement of A1 receptors or KATP channels during early stages in the development of ischemic tolerance in vivo, and emphasize the need for robust, well-controlled, and quantitative models in such studies.