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Halothane and isoflurane decrease the open state probability of K+ channels in dog cerebral arterial muscle cells
H Eskinder1, D Gebremedhin, J G Lee
1Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226.
Anesthesiology
|February 1, 1995
Summary
Volatile anesthetics like halothane and isoflurane suppress K+ channel activity in dog cerebral arteries. This suggests other mechanisms are responsible for anesthetic-induced vasodilation.
Area of Science:
- Neuroscience
- Pharmacology
- Physiology
Background:
- Volatile anesthetics (halothane, isoflurane) cause cerebral vasodilation.
- A potential mechanism involves increased K+ efflux via enhanced K+ channel opening frequency.
- This study investigated anesthetic effects on K+ channel currents in canine cerebral artery smooth muscle cells.
Purpose of the Study:
- To determine the effects of halothane and isoflurane on K+ channel currents.
- To elucidate the role of K+ channels in volatile anesthetic-induced cerebral vasodilation.
Main Methods:
- Utilized patch clamp recording techniques (whole-cell and cell-attached configurations).
- Investigated macroscopic and microscopic K+ channel currents.
- Examined effects of tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on K+ currents.
Main Results:
- Halothane (0.4-0.9 mM) reduced outward K+ current amplitude by 18-34% in whole-cell mode.
- A Ca2+-activated K+ channel (99 pS conductance) was identified in cell-attached patches.
- Halothane and isoflurane decreased the open state probability and opening frequency of this K+ channel, without altering single channel amplitude.
Conclusions:
- Halothane and isoflurane suppress the activity of K+ channels in canine cerebral arterial smooth muscle cells.
- These findings indicate that K+ channel suppression, not activation, occurs with these anesthetics.
- Mechanisms independent of K+ channel opening likely mediate volatile anesthetic-induced cerebral vasodilation.