Effect of chronic morphine exposure on the synaptic plasma‐membrane subproteome of rats: a quantitative protein profiling study based on isotope‐coded affinity tags and liquid chromatography/mass spectrometry

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Abstract
The effect of chronic morphine exposure on the synaptic plasma‐membrane subproteome in rats was studied by the isotope‐coded affinity tag (ICAT) method coupled with capillary reversed‐phase liquid chromatography/electrospray ionization mass spectrometry and tandem mass spectrometry. ICAT‐labeled tryptic peptides of synaptic membrane proteins were successfully identified using tandem mass spectrometry in conjunction with protein database searching. Several important synaptic plasma‐membrane proteins displayed significant regulation changes as a result of chronic morphine exposure in vivo. In particular, an integral membrane protein Na+/K+ ATPase (α‐subunit) involved in regulation of the cell membrane potential by controlling sodium and potassium ion permeability was downregulated by 39 ± 2%. This result was in excellent agreement with the reduction in electrogenic Na+, K+ pumping due to about 40% downregulation of Na+/K+ ATPase α3‐isoform in myenteric S‐neurons of morphine‐exposed guinea‐pigs measured by others via immunohistochemistry. The decrease in the abundance of non‐erythroid αII‐spectrin in the synaptic plasma‐membrane fraction was also observed, which was hypothetically associated with the breakdown of the protein due to the upregulation of the proteolytic enzyme caspase‐3 upon chronic morphine exposure. Copyright © 2005 John Wiley & Sons, Ltd.