Calcium-activated K+ channels in cerebral arterioles in piglets are resistant to ischemia.
Our previous studies indicate that function of ATP-dependent K+ channels (K(ATP)) in cerebral arterioles is suppressed after ischemia. In the current study, we examined pial arteriolar responses to forskolin, dibutyryl-cAMP, NS-1619, and methionine (met)-enkephalin, activators of calcium-dependent K+ channels (K(Ca)) before and 1 hour after 10 minutes of total, global ischemia in anesthetized piglets. Arteriolar diameters were measured using a closed cranial window and intravital microscopy. All pharmacologic agents were given topically. Baseline diameters were approximately 100 microm, and diameters had returned to normal by 1 hour after ischemia. Forskolin dilated arterioles by 9 +/- 3%, 18 +/- 4%, and 31 +/- 12% at 5 x 10(-8), 5 x 10(-7), and 10(-6) mol/L, respectively (P < 0.05, n = 10). In addition, dibutyryl-cAMP dilated arterioles by 8 +/- 2% at 10(-4) mol/L and 14 +/- 2% at 3 x 10(-4) mol/L (P < 0.05, n = 6). Also, NS-1619 increased diameter of arterioles by 9 +/- 2% at 10(-7) mol/L and 17 +/- 9% at 10(-5) mol/L (P < 0.05, n = 5). Finally, met-enkephalin dilated arterioles by 9 +/- 2% at 10(-8) mol/L and 16 +/- 3% at 10(-6) mol/L (P < 0.05, n = 5). At 1 hour after ischemia, arteriolar dilator effects to forskolin, dibutyryl-cAMP and NS-1619, and met-enkephalin were intact. Thus, in contrast to K(ATP), K(Ca) in cerebral arterioles are resistant to ischemic stress.
Bari
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F
Department of Physiology and Pharmacology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1083, U.S.A.
Louis
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TM
Busija
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DW
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001160:Arterioles / Q000187:drug effects / Q000378:metabolism; D002545:Brain Ischemia / Q000503:physiopathology*; D002118:Calcium / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D015221:Potassium Channels / Q000502:physiology*; D013552:Swine; D014664:Vasodilation / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology
D015221:Potassium Channels; D014665:Vasodilator Agents; D002118:Calcium