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The volatile anesthetic isoflurane attenuates Ca++ mobilization in cultured vascular smooth muscle cells
Abstract:
Isoflurane is a volatile anesthetic which decreases vascular tone. Experiments were designed to determine whether isoflurane attenuated agonist-induced signaling in cultured vascular smooth muscle cells (A7r5). Cells were preincubated for 15 to 20 min with clinically relevant concentrations of isoflurane--0.5 to 2% in the gas phase and stimulated with 10(-9) or 10(-7) M vasopressin or with 3.3 x 10(-9) M platelet-derived growth factor. The two agonists are believed to act via differing signaling pathways. Total inositol phosphate formation was measured by column chromatography. Apparent intracellular free Ca++ concentration (1) [Ca++]i was estimated using indo-1 and flow cytometry. Isoflurane attenuated increases in [Ca++]i evoked by both agonists. Isoflurane 2.0% inhibited [Ca++]i responses evoked by vasopressin by 35 to 41%. Responses due to Ca++ release from intracellular stores were particularly sensitive to inhibition by isoflurane. The anesthetic attenuated inositol phosphate generation evoked by vasopressin and platelet-derived growth factor, suggesting a mechanism for isoflurane action on Ca++ release. Surprisingly, the anesthetic only modestly inhibited increases in [Ca++]i due to Ca++ entry. Isoflurane's effect on Ca++ influx after emptying of Ca++ stores was probed using thapsigargin. Inhibition of Ca++ influx was modest. It is suggested that isoflurane attenuates total inositol phosphate formation and Ca++ release evoked by vasopressin and platelet-derived growth factor while having limited effects on agonist-induced Ca++ entry.
Insights
Isoflurane, an anesthetic, reduces vascular smooth muscle cell responses to vasopressin and platelet-derived growth factor. It primarily inhibits calcium release, with limited effects on calcium entry.
Area of Science:
- Pharmacology
- Cell Biology
- Anesthesiology
Background:
- Isoflurane is a volatile anesthetic known to decrease vascular tone.
- Vascular smooth muscle cells (A7r5) are crucial for regulating blood pressure.
- Agonist-induced signaling pathways in vascular smooth muscle are complex and involve calcium dynamics.
Purpose of the Study:
- To investigate the effects of isoflurane on agonist-induced signaling in cultured vascular smooth muscle cells.
- To determine if isoflurane attenuates signaling pathways activated by vasopressin and platelet-derived growth factor.
- To elucidate the specific mechanisms of isoflurane's action on intracellular calcium mobilization and inositol phosphate formation.
Main Methods:
- Cultured A7r5 vascular smooth muscle cells were preincubated with clinically relevant concentrations of isoflurane (0.5-2%).
- Cells were stimulated with vasopressin or platelet-derived growth factor, agonists acting via distinct signaling pathways.
- Intracellular calcium ([Ca++]i) was measured using indo-1 and flow cytometry; total inositol phosphate formation was assessed via column chromatography.
Main Results:
- Isoflurane significantly attenuated agonist-induced increases in intracellular calcium ([Ca++]i), with 2.0% isoflurane inhibiting vasopressin-evoked responses by 35-41%.
- Responses mediated by calcium release from intracellular stores were particularly sensitive to isoflurane.
- Isoflurane inhibited inositol phosphate generation by both vasopressin and platelet-derived growth factor, suggesting a role in modulating calcium release pathways. Effects on agonist-induced calcium entry were modest.
Conclusions:
- Isoflurane attenuates agonist-induced total inositol phosphate formation and calcium release in vascular smooth muscle cells.
- The anesthetic exhibits limited inhibitory effects on agonist-induced calcium entry.
- These findings suggest that isoflurane's impact on vascular tone may be partly mediated by its interference with intracellular calcium signaling pathways, particularly calcium release mechanisms.