Gx/z is regulated by mu but not delta opioid receptors in the stimulation of the low Km GTPase activity in mouse periaqueductal grey matter.

High affinity low K(m) GTPase activity was measured in membrane preparations of adult mouse mesencephalic periaqueductal grey matter (PAG). Opioids displaying selectivity towards mu- or delta-opioid receptors (OR) activated the enzyme in a concentration-dependent manner. Antibodies to mu-OR greatly impaired the potential of mu-agonists, [D-Ala2,N-MePhe4,Gly-ol5]-enkephalin (DAMGO) and morphine, to increase hydrolysis of GTP. The same antibodies had little effect on [D-Pen2,5]enkephalin (DPDPE) and [D-Ala2]deltorphin II, both agonists at delta-OR. Stimulation of GTPase by DPDPE and [D-Ala2]deltorphin II - but not by morphine or DAMGO - was diminished by antibodies to delta-OR. The blockade of G(i2)alpha subunits by specific antibodies impaired the activation of G alpha-related GTPase by all opioids. Antibodies in vitro, and oligodeoxynucleotides in vivo, prepared against Gx/z alpha subunits, reduced the release of Pi promoted by DAMGO and morphine. The impairment of Gx/z proteins also slightly reduced the effect of the delta2 agonist [D-Ala2]deltorphin II. At delta1 receptors, DPDPE fully expressed its activation of GTPase. These results indicate that in the PAG, mu-OR and delta-OR couple with Gi2 transducer proteins. Notably, mu-OR also regulates the pertussis toxin-insensitive G-protein Gx/z, an effect poorly exhibited by delta-OR in this tissue.