INWARD RECTIFIER POTASSIUM CHANNELS IN THE RAT MIDDLE CEREBRAL-ARTERY

Inward rectifier K+ channels (K(ir)s) were studied in the isolated per fused rat middle cerebral artery (MCA). The addition of 15 mM K+ (KCl) to the extraluminal bath dilated the MCAs. These dilations were block ed by selective inhibitors for the K(ir)s (40 mu M BaCl2 or 40 mM CsCl ) but not selective inhibitors for other K+ channels (glibenclamide, t etraethylammonium, or 4-aminopyridine). Neither removal of the endothe lium nor treatment with the nitric oxide synthase inhibitor (N-G-nitro -L-arginine methyl ester, 10 mu M) affected the K+-induced dilation. T he addition of BaCl2 to resting MCAs produced a dose-dependent constri ction of 8-12%, indicating that, during resting conditions, K(ir)s aid in setting or determining the resting tone. The magnitude of the dila tions produced by the addition of K+ or constrictions produced by BaCl 2 were independent of pressure over a range of 40-100 mmHg. We conclud e that K(ir)s, which produce a dilation when activated, exist on the v ascular smooth muscle of the rat MCA. These K(ir)s aid in determining the resting tone of the vessel, and their function is independent of p ressure over physiological pressure ranges.