Effect of ibudilast on in vitro ischemia-induced calcium mobilization in gerbil hippocampal slices

Evaluation using microfluorometry

Abstract

We examined, by microfluorometry, whether or not 3-isobutyryl-2-isopropylpyrazolo [1, 5-a] pyridine (ibudilast) has any effect on in vitro ischemia-induced rises of intracellular Ca²⁺ concentration ([Ca²⁺] _i) in the CA1 field of gerbil hippocampal slices. Transverse hippocampal slices (300 μm-thick) were loaded with rhod-2, a calcium ion-sensitive dye, and then transferred to a flow-through chamber mounted on an inverted fluorescence microscope. The changes in [Ca²⁺] _i were measured using an intracellular calcium ion imaging system. When the slices were exposed to a glucose-free physiological medium equilibrated with a 95% N₂/5% CO₂ gas mixture (standard in vitro ischemic conditions), a large [Ca²⁺] _i elevation was detected about 5 min after the beginning of the standard in vitro ischemic conditions. Howerver, the extent of in vitro ischemia-induced [Ca²⁺] _i increase in the presence of 43 μM ibudilast was significantly depressed in all subregions of the hippocampal slices as compared with that under standard in vitro ischemic conditions. Similar [Ca2²⁺] _i increases in the CA1 field were induced by Ca²⁺-free in vitro ischemic conditions, a high concentration of KCl or each specific agonist for the glutamate receptor subtypes, N-methyl-D-aspartate, (s) -alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and kainate; and these increases were also depressed in the presence of 43 μM ibudilast in the perfusion medium. The above findings indicate that ibudilast exerts an inhibitory effect on the in vitro ischemia-induced [Ca²⁺] _i elevation and that this inhibitory effect is caused by decreases in Ca²⁺ influx through the agonist-gated Ca²⁺ channels and also the voltage-gated Ca²⁺ channels as well as in Ca²⁺ release from the intracellular Ca²⁺ stores. The present inhibitory effect of ibudilast on Ca²⁺ accumulation may be involved in the mechanisms whereby ibudilast can diminish ischemic injury in hippocampal CA1 neurons.