Effect of volatile anesthetics with and without verapamil on intracellular activity in vascular smooth muscle.
BACKGROUND
Although halothane and isoflurane inhibit receptor agonist-induced smooth muscle contraction by inhibiting Ca2+ influx via the L-type voltage-dependent Ca2+ channels, their effects on pharmacomechanical coupling remained to be clarified. The intracellular action of both anesthetics was studied during agonist-induced contractions using the Ca2+ channel blocker verapamil.


METHODS
Isolated spiral strips of rat thoracic aorta with endothelium removed were suspended for isometric tension recordings in physiologic salt solution. Cytosolic concentration of Ca2+ ([Ca2+]i) was measured concomitantly using fura-2-Ca2+ fluorescence. Muscle contraction was evoked by the receptor agonists with 30 nm norepinephrine or 10 microM prostaglandin F2 alpha (PGF2 alpha), followed by exposure to halothane, at 0%, 1%, 2%, and 3% or isoflurane, at 2% and 4%. The effects of the anesthetics were compared with those of 0.1-1 microM verapamil (n = 8 for each condition). To clarify the intracellular action of the volatile anesthetics on agonist-induced contractions, this procedure was repeated for the anesthetics only in the presence of 1 microM verapamil (n = 8 for each condition). The effects of both anesthetics were also examined in nonreceptor-mediated contractions evoked with a 1-microM dose of the protein kinase C activator, 12-deoxyphorbol 13-isobutylate, which increases the Ca2+ sensitivity of the contractile elements (n = 8 for each).


RESULTS
Halothane, isoflurane, and verapamil suppressed norepinephrine-and PGF2 alpha-induced increases in muscle tension and [Ca2+]i in a concentration-dependent manner. The Ca2+-tension regression lines suggested that the volatile anesthetics reduced Ca2+ sensitivity of the contractile elements during PGF2 alpha-induced contraction. Pretreatment of the muscle strip with verapamil revealed that halothane and isoflurane released Ca2+ during norepinephrine-induced contraction and that [Ca2+]i-tension relationship was modulated during PGF2 alpha-induced contractions. Halothane at 2% and 3% and isoflurane at 4% suppressed 12-deoxyphorbol 13-isobutylate-induced increases in muscle tension, whereas they enhanced increases in [Ca2+]i, indicating that both anesthetics suppressed Ca2+ sensitivity during 12-deoxyphorbol 13-isobutylate-induced contraction.


CONCLUSIONS
Verapamil pretreatment unmasked the intracellular action of the anesthetics. Halothane and isoflurane influenced pharmacomechanical coupling during agonist-induced contraction.
Namba
H
H
Department of Anesthesiology, Sapporo Medical University School of Medicine, Japan.
Tsuchida
H
H
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015237:Dinoprost / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D006221:Halothane / Q000494:pharmacology; D066298:In Vitro Techniques; D007530:Isoflurane / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014661:Vasoconstriction / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology*
D018685:Anesthetics, Inhalation; D002121:Calcium Channel Blockers; D015237:Dinoprost; D014700:Verapamil; D007530:Isoflurane; D002118:Calcium; D006221:Halothane; D004837:Epinephrine