The introduction of inhalational anesthetics a century and a half ago marks a major medical and pharmacologic achievement. Neuronal membranes are favored as a likely site of anesthetic effect, either by biophysical interaction of anesthetics with membrane lipids or by induction of conformational changes in membrane proteins. Clinical anesthesia probably results from interference with information transfer at the synaptic level of brain organization. The overall objective of this proposal is to test the hypothesis that anesthetics interfere with synaptic transmission by altering lipid modulation of the Ca++-ATPase pump. There is good evidence that enzymatic methylation of membrane phospholipids does modulate transduction of biologic signals across cell membranes. Studies from our laboratory show that halothane and isoflurane stimulate phospholipid methylation (PLM) as much as two fold in rat brain synaptosomes. More recent work shows a reduction in Ca++-ATPase pump activity in synaptosomal plasma membrane (SPM) obtained from cerebra, cerebella, midbrains and medullae of rats anesthetized with halothane. This reduction varies from 25% to 75%, with the greatest inhibition seen in the medulla. Pump activity returns to control levels in SPM from rats allowed to recover from anesthesia.
The first aim of this proposal is to define characteristics of the calcium pump response to halothane. Dose response of Ca++ pump activity in synaptosomal plasma membranes will be evaluated at halothane concentrations ranging from 0.5 to 2.0%. We recently observed significant PLM stimulation over a wide range of halothane dosage. Possible concomitant halothane effects on SPM gated Ca++ channels and pump activity will also be tested. Linkage of PLM to the calcium pump response to halothane will be examined in experiments in which PLM can be inhibited or stimulated. A large effort will be directed toward testing for calmodulin, lipid, Ca++-ATPase interaction in the anesthetic response. We propose to assess anesthetic effects on Ca++ pump activity in calmodulin depleted and repleted SPM and to study anesthetic effects on purified and reconstituted rat brain Ca++-ATPase.
A second aim i s to determine where and how inhalational anesthetics affect the PLM pathway. Selective enzyme assays and kinetic studies will be used to identify putative, irreversible changes in methylating enzymes resulting from anesthetic exposure.
A third aim i s to evaluate the generality of calcium pump and PLM responses to anesthetics.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM046401-03
Application #
2183866
Study Section
Surgery, Anesthesiology and Trauma Study Section (SAT)
Project Start
1992-08-01
Project End
1996-06-30
Budget Start
1994-08-01
Budget End
1996-06-30
Support Year
3
Fiscal Year
1994
Total Cost
Indirect Cost
Name
Vanderbilt University Medical Center
Department
Anesthesiology
Type
Schools of Medicine
DUNS #
004413456
City
Nashville
State
TN
Country
United States
Zip Code
37212
Franks, J J; Wamil, A W; Janicki, P K et al. (1998) Anesthetic-induced alteration of Ca2+ homeostasis in neural cells: a temperature-sensitive process that is enhanced by blockade of plasma membrane Ca2+-ATPase isoforms. Anesthesiology 89:149-64
Horn, J L; Janicki, P K; Singh, G et al. (1996) Reduced anesthetic requirements in aged rats: association with altered brain synaptic plasma membrane Ca(2+)-ATPase pump and phospholipid methyltransferase I activities. Life Sci 59:PL263-8
Janicki, P K; Horn, J L; Singh, G et al. (1996) Increased anesthetic requirements for isoflurane, halothane, enflurane and desflurane in obese Zucker rats are associated with insulin-induced stimulation of plasma membrane Ca(2+)-ATPase. Life Sci 59:PL269-75
Franks, J J; Horn, J L; Janicki, P K et al. (1995) Halothane, isoflurane, xenon, and nitrous oxide inhibit calcium ATPase pump activity in rat brain synaptic plasma membranes. Anesthesiology 82:108-17
Horn, J L; Janicki, P K; Franks, J J (1995) Diminished brain synaptic plasma membrane Ca(2+)-ATPase activity in spontaneously hypertensive rats: association with reduced anesthetic requirements. Life Sci 56:PL427-32
Janicki, P K; Horn, J L; Singh, G et al. (1995) Reduced anesthetic requirements, diminished brain plasma membrane Ca(2+)-ATPase pumping, and enhanced brain synaptic plasma membrane phospholipid methylation in diabetic rats: effects of insulin. Life Sci 56:PL357-63
Horn, J L; Janicki, P K; Franks, J J (1995) Nitrous oxide and xenon enhance phospholipid-N-methylation in rat brain synaptic plasma membranes. Life Sci 56:PL455-60
Singh, G; Janicki, P K; Horn, J L et al. (1995) Inhibition of plasma membrane Ca(2+)-ATPase pump activity in cultured C6 glioma cells by halothane and xenon. Life Sci 56:PL219-24
Janicki, P K; Horn, J L; Singh, G et al. (1994) Diminished brain synaptic plasma membrane Ca(2+)-ATPase activity in rats with streptozocin-induced diabetes: association with reduced anesthetic requirements. Life Sci 55:PL359-64