Tygon Microbore Tubing Releases a Non-competitive Inhibitor of GABA_A Receptors

Alison Althaus
Marquette University
Mentor:  Dr. David Wagner

GABA is the major inhibitory neurotransmitter in the vertebrate central nervous system.  The GABA_A receptor is a hetero-pentameric integral membrane protein. When GABA binds to the GABA_A receptor, a central pore opens that allows chloride ions to cross the cell membrane; usually resulting in hyper-polarization. The most common type of GABA_A receptor is thought to be composed of 2 ? subunits, 2 ? subunits and 1 ? subunit.  However, a ? subunit is not required for function, and receptors with a stoichiometry of 2 ? and 3 ? subunits can be expressed in heterologous systems.  GABA-evoked chloride currents in ???? subunit-containing receptors have a consistent and predictable shape when GABA and wash solutions are administered through PE, PTFE, Fiberglass, and various other types of tubing.  GABA-evoked currents measured when solutions flow through Tygon microbore tubing do not exhibit this same predictable shape.  We believe this effect is due to the release of an unidentified compound (T-factor) from the Tygon microbore tubing.

T-factor exerts several effects on GABA-evoked currents; it decreases peak current amplitude while increasing the rate and extent of fast desensitization.  On concurrent removal of both GABA and T-factor, the GABA-evoked current regenerates.  This suggests that T-factor unbinds more quickly than GABA and that the two compounds do not share a common binding site.  Therefore, T-factor is not a competitive antagonist.  This conclusion is also supported by the fact that saturating pre-incubation in T-factor does not fully block GABA-evoked currents.  In order to gauge the effect of sub-saturating T-factor, “length-response” experiments were also performed. 
 
 
 
 

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