The sensitivity of opioid receptor types to regulation by sodium and GTP
The effects of Na+ and GTP on agonist binding to μ, δ, and κ opioid binding sites in membranes from guinea pig cortex have been studied. All incubations were in a modified Krebs-Hepes buffer at 37°; effects of Na+ were evaluated by replacement with an equal concentration of K+. μ binding sites appeared more sensitive than δ sites, while κ sites were the least sensitive to both regulators. However, even at κ sites, Na+ induced a significant reduction in agonist affinity and GTP caused a significant reduction in maximum binding. © 1984.
Werling, L., Brown, S., & Cox, B. (1984). The sensitivity of opioid receptor types to regulation by sodium and GTP. Neuropeptides, 5 (1-3). http://dx.doi.org/10.1016/0143-4179(84)90046-5