Mechanisms of isoflurane-mediated  hyperpolarization of vascular smooth muscle in chronically hypertensive and normotensive conditions.
BACKGROUND
The purpose of this study was to compare the effects of isoflurane on membrane and intracellular mechanisms that regulate vascular smooth muscle (VSM) transmembrane potential (Em; which is related to VSM tone) in the spontaneously hypertensive rat (SHR) model of essential hypertension and its normotensive Wistar-Kyoto (WKY) control.


METHODS
Vascular smooth muscle Em values were measured in situ in locally denervated, superfused, intact, small (200-300-microm OD) mesenteric arteries and veins in anesthetized 9-12-week-old SHR and WKY. Effects of 1.0 minimum alveolar concentration (0.60 mM) superfused isoflurane on VSM Em were measured before and during superfusion with specific inhibitors of VSM calcium-activated (KCa) and adenosine triphosphate-regulated (KATP) potassium channels, and with endogenous mediators of vasodilatation (nitric oxide, cyclic guanosine monophosphate, protein kinase G, cyclic adenosine monophosphate, and protein kinase A).


RESULTS
Isoflurane significantly hyperpolarized small arteries (5 +/- 3.4 mV) and veins (6 +/- 4.7 mV) (pooled SHR and WKY, mean +/- SD). Inhibition of KCa and KATP channels, cyclic adenosine monophosphate, and protein kinase A, but not nitric oxide, cyclic guanosine monophosphate, and protein kinase G, abolished such hyperpolarization equally in SHR and WKY vessels.


CONCLUSIONS
Isoflurane-induced in situ VSM hyperpolarization in denervated, small mesenteric vessels involves a similar activation of KCa and KATP channels and cyclic adenosine monophosphate, but not nitric oxide or cyclic guanosine monophosphate, second messenger pathways in both SHR and WKY. A greater isoflurane-induced VSM hyperpolarization (observed previously in neurally intact SHR vessels) suggests enhanced inhibition of elevated sympathetic neural input as a major mechanism underlying such hyperpolarization (and coupled relaxation) in this neurogenic model of hypertension.
Stekiel
T A
TA
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA. tstekiel@mcw.edu
Contney
S J
SJ
Kokita
N
N
Bosnjak
Z J
ZJ
Kampine
J P
JP
Stekiel
W J
WJ
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000242:Cyclic AMP / Q000037:antagonists & inhibitors; D006152:Cyclic GMP / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007530:Isoflurane / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D026902:Potassium Channel Blockers; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY
D018685:Anesthetics, Inhalation; D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D007530:Isoflurane; D000242:Cyclic AMP; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester