Na+, K+ ATPase α-subunit isoform distribution and abundance in guinea-pig longitudinal muscle/myenteric plexus after exposure to morphine

Previous work in the myenteric plexus has shown that the resting membrane potential of morphine-tolerant guinea-pig myenteric S neurons is significantly depolarized relative to placebo-implanted controls, and that this depolarization is associated with reduced electrogenic Na+. K+ pumping. Identification of the subunits of the sodium pump which are in the myenteric plexus Was undertaken in order to facilitate direct qualitative and quantitative measurements of the abundance of sodium pump isoforms after morphine exposure, thereby confirming and extending the electrophysiological data to the Molecular level. Seven days prior to the experiments, tolerance was induced by subcutaneous implantation of morphine pellets (one pellet. 75 mg/100 L, bode weight) while control guinea pigs received placebo pellets. Using immunohistochemistry and confocal microscopy, the distribution of the alpha Subunit isoforms of the Na+/K+-ATPase in placebo and morphine-tolerant guinea-pig ileum was determined. Only the alpha, and alpha(s) subunit isoforms Acre in Sufficient abundance to be observed. The alpha(1) subunit isoform was most highly concentrated in the mucosa and in neurons. In contrast, the alpha, subunit isoform was uniquely localized to neurons. Western and slot blot analyses of longitudinal muscle/myenteric plexus homogenates identified a significant reduction of the alpha(0) but not the alpha(1) subunit isoform in tolerant preparations. It is concluded that the reduced electrogenic pumping in the S neurons after morphine exposure is associated with a reduction in the alpha(3) subunit isoform. (C) 2002 Elsevier Science B.V. All rights reserved.