P-glycoprotein (ABCB1/MDR1, EC 3.6.3.44), the major efflux transporter at the blood-brain barrier (BBB), is a formidable obstacle to CNS
pharmacotherapy. Understanding the mechanism(s) for increased
P-glycoprotein activity at the BBB during peripheral inflammatory
pain is critical in the development of novel strategies to overcome the significant decreases in CNS
analgesic drug delivery. In this study, we employed the λ-
carrageenan pain model (using female Sprague-Dawley rats), combined with confocal microscopy and subcellular fractionation of cerebral microvessels, to determine if increased
P-glycoprotein function, following the onset of peripheral inflammatory
pain, is associated with a change in
P-glycoprotein trafficking which leads to
pain-induced effects on
analgesic drug delivery. Injection of λ-
carrageenan into the rat hind paw induced a localized, inflammatory
pain (
hyperalgesia) and simultaneously, at the BBB, a rapid change in colocalization of
P-glycoprotein with
caveolin-1, a key scaffolding/trafficking
protein. Subcellular fractionation of isolated cerebral microvessels revealed that the bulk of
P-glycoprotein constitutively traffics to membrane domains containing high molecular weight,
disulfide-bonded
P-glycoprotein-containing structures that cofractionate with membrane domains enriched with monomeric and high molecular weight,
disulfide-bonded, caveolin-1-containing structures. Peripheral inflammatory
pain promoted a dynamic redistribution between membrane domains of
P-glycoprotein and
caveolin-1. Disassembly of high molecular weight
P-glycoprotein-containing structures within microvascular endothelial
luminal membrane domains was accompanied by an increase in
ATPase activity, suggesting a potential for functionally active
P-glycoprotein. These results are the first observation that peripheral inflammatory
pain leads to specific structural changes in
P-glycoprotein responsible for controlling
analgesic drug delivery to the CNS.