Spreading depolarization evoked by endothelin-1 is inhibited by octanol but not by carbenoxolone

Abstract

Spreading depolarization (SD) has been implicated in the pathogenesis of delayed cerebral ischemia (DCI) after subarachnoid hemorrhage. Endothelin-1 (ET-1) is a powerful trigger of SD and may be involved in DCI. The SD-causing mechanism is assumed to result from ET-1-induced microarterial spasm and ischemia. However, ET-1 is also a potent, astrocyte-specific gap junction (GJ) inhibitor. There are two competing hypotheses on the role of astrocytic GJs in SD. One postulates that they mediate SDs, since long-chain alcohols such as octanol inhibit GJs and inhibit SD at high concentrations. The other postulates that astrocytic GJs protect against SD and that their inhibition increases susceptibility to SD and SD velocity. Here, we found in rats that brain topical application of carbenoxolone, a more specific GJ inhibitor, failed to inhibit ET-1-induced SDs in vivo, whereas octanol, a less specific GJ inhibitor, partially blocked them at high concentrations. These results suggest that GJs are not required for initiation or propagation of ET-1-induced SDs, and that octanol inhibits SDs by effects unrelated to GJs. The results do not exclude that the specific inhibition of astrocytic GJs by ET-1 contributes to the generation of SDs, which should be further investigated in future studies.