ROLE OF ATP-SENSITIVE POTASSIUM CHANNELS IN BRAIN-STEM CIRCULATION DURING HYPOTENSION

The basilar artery and its branch arterioles dilate actively in respon se to a marked decrease in blood pressure and maintain cerebral blood flow (CBF) to the brain stem. We tested the hypothesis that ATP-sensit ive potassium (K-ATP) channels play a role in the autoregulatory respo nses of the brain stem circulation in vivo. In anesthetized Sprague-Da wley rats, local CBF to the brain stem was determined with laser-Doppl er flowmetry, and diameters of the basilar artery and branch arteriole s were measured through a cranial window during stepwise hemorrhagic h ypotension. During topical application of 10(-6) and 10(-5) mol/l of g libenclamide, a selective K-ATP-channel blocker, the lower limit of CB F autoregulation shifted upward to 60-75 from 30-45 mmHg in the vehicl e group. Glibenclamide significantly impaired the dilator response of small arterioles (baseline diameter 45 +/- 2 mu m) throughout hypotens ion (P < 0.03) but did not impair the dilatation of the basilar artery (247 +/- 3 mu m) or large arterioles (99 +/- 4 mu m). Thus K-ATP chan nels appear to play an important role in the regulation of CBF to the the brain stem during hypotension by mediating the compensatory dilata tion of small arterioles. In contrast, these channels may not be a maj or regulator of the vascular tone of larger arteries during hypotensio n.