Halothane inhibits agonist-induced inositol phosphate and Ca2+ signaling in A7r5 cultured vascular smooth muscle cells.
Halothane, an anesthetic with marked depressant effects on the circulation, was studied for its ability to inhibit inositol phosphate and Ca2+ signaling evoked by the vasoactive hormone arginine vasopressin (AVP) and Ca2+ responses elicited by platelet-derived growth factor and by thapsigargin in cultured A7r5 vascular smooth muscle cells. Changes in apparent [Ca2+]i were measured using the indicator indo-1 and flow cytometry, whereas inositol phosphate levels were determined using myo-[3H]inositol and column chromatography. Preincubation with clinically relevant concentrations of halothane resulted in dose-dependent depression of [Ca2+]i responses evoked on stimulation with AVP. Halothane (2.0%) inhibited the increases in [Ca2+]i by 34-45%. In cells incubated in Ca(2+)-free medium plus 0.5 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, the halothane effect was more marked, with 1.5% halothane inhibiting the responses by approximately 53-61%. However, when Ca2+ influx was stimulated by addition of 5 mM Ca2+ in the continued presence of the agonist, the [Ca2+]i response was inhibited by only 15%, suggesting that release of Ca2+ rather than Ca2+ influx is more sensitive to inhibition by the anesthetic. The effects of halothane on Ca2+ homeostasis are not explained solely by anesthetic-induced depletion of Ca2+ from intracellular stores, because the anesthetic inhibited increases in [Ca2+]i elicited by thapsigargin in cells suspended in Ca(2+)-free medium by only 31%. Halothane inhibited inositol phosphate formation elicited by AVP, suggesting an additional means by which the anesthetic may alter agonist-induced Ca2+ responses. The current results also demonstrate that halothane actions are not specific solely to responses evoked by AVP, which acts via a guanine nucleotide-binding protein-linked signaling pathway, but include responses stimulated by platelet-derived growth factor, an agonist that elevates [Ca2+]i via receptor-latent tyrosine kinase activity. The current results demonstrate that, in vascular smooth muscle cells, halothane alters Ca2+ homeostasis, an action that may underlie the in vivo vasodilator effects of the anesthetic.
Sill
J C
JC
Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905.
Uhl
C
C
Eskuri
S
S
Van Dyke
R
R
Tarara
J
J
D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media; D006221:Halothane / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000096:biosynthesis / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013268:Stimulation, Chemical; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013997:Time Factors
D003470:Culture Media; D007295:Inositol Phosphates; D010982:Platelet-Derived Growth Factor; D013729:Terpenes; D001127:Arginine Vasopressin; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium; D006221:Halothane