# Presentation: 210721

## Sites of Action for Abused Inhalants

- John J Woodward
- Professor, Dept. of Neurosciences; Center for Drug and Alcohol Programs
- Medical University of South Carolina
- Charleston, SC

## Abused Inhalants

- -Represent a diverse set of compounds found in a variety of products
- 	•Volatile alkyl nitrites-amyl, butyl nitrite
- 	•Gases-butane,propane,fluorohydrocarbons
- 	•Volatile solvents-paint thinner,gasoline,glues, 	correction fluids
- -Neuronal sites of action largely unknown

## Lipid versus Protein Sites of Action

- Meyer-Overton
- Anesthetic potency positively correlated with lipid solubility; “membrane fluidity”
- -Challenges to Lipid Theory
- Greater effects on synaptic versus axonal transmission
- Development of compounds with high lipid solubility that are behaviorally inert
- Meyer-Overton dynamics preserved in luciferase; a lipid-free protein
*Suggests that brain proteins involved in synaptic transmission are potential targets for volatile CNS depressants*

## Gap Junctions-Connexins

- Assembled from Connexin proteins (Cx 32, 45, etc.)
- Allow intercellular passage of ions, metabolites and 2nd messengers < 1 kDa
- Electrical coupling (epithelium, cardiac syncitium, neurons)
- Developmental role (neuronal migration, differentiation, deafness, cataracts, skin disorders)

## Toluene Inhibits Gap Junctions Expressed in HEK Cells

*Del Re and Woodward, 2005*

## Voltage-Sensitive Calcium Channels Are Both Potentiated and Inhibited by Toluene and Related Solvents

*Shafer et al., 2005*

## Calcium-Activated Potassium Channels (BK)

- Voltage dependent
- Calcium activated (calcium bowl / RCK)
- Located pre-synaptically and post-synaptically and are responsible for fAHP
- Potentiated by ethanol

## BK Channels Expressed in Oocytes

*Del Re and Woodward*

## Toluene and Etoh Have Opposing Actions on BK Channels Expressed in Oocytes

*Del Re and Woodward*

## GirK 1-4 subunits

- 2 TM regions
- 4 subunits comprise a functional channel
- GirK 2 and 1/2 are neuronal; GirK 1/4 cardiac
- Multiple  binding domains
- PIP2 binding domain
- Potentiated by ethanol
- Inhibited by volatile anesthetics - halothane & isoflurane

- G-protein Inwardly Rectifying K Channels (GirK)

## G-protein Inwardly Rectifying K Channels (GirK) Expressed in Oocytes

- GirK 2-brain
- GirK 1/4-cardiac

## Toluene Inhibits G-protein Inwardly Rectifying K Channels (GirK)

- 0

- 10

- 20

- 30

- 1

**% Inhibition by Toluene**

- GIRK 2

- GIRK 1/2

- GIRK 1/4

- 3 mM Toluene

- 1 mM Toluene

- *

- *

*D*

- _Receptor Combination_

*Del Re and Woodward*

## G-protein Inwardly Rectifying K Channels (GirK) Are Activated by a Variety of G-protein Linked Receptors (GPCR)

- hK

- Glu

- Glu

- I

*A*

- Tol

- Tol

- Glu

- hK

*B*

*Del Re and Woodward*

## Toluene Inhibition of GirK Channels is Not Altered by GPCR Activation

- 0

- 5

- 10

- 15

- 20

- 25

- 30

- 35

- 40

- 1

**% Inhibition by Toluene**

- 3 mM Toluene

- 1 mM Toluene

-         GirK 2 /mGluR1

- GirK 2

*C*

- _Receptor Combination_

*Del Re and Woodward*

## Summary of the Effects of Toluene on Ion Channel Function

- Inhibition

- No Effect

- Potentiation

- GABA ; Glycine 
- Non-NMDA (10 mM)
- P2X2, 4

- AMPA (GluR1-4)
- GirK 1/4

- VSCC
- L-type    Non L-type

- *from other investigators

*Supported by NIDA DA13951*