Irradiation inactivation studies of the dopamine D1 receptor and dopamine-stimulated adenylate cyclase in rat striatum

In frozen rat striatal tissue, exposed to 10 MeV electrons from a linear accelerator, the sizes of the dopamine (DA) D1 receptor and the DA sensitive adenylate cyclase complex were determined using target size analysis. The number of D1 receptors (labelled by [3H]SCH 23390)declined monoexponentially with increasing radiation intensity, yielding a molecular weight (mol. wt.) of 80kDa. Also the activity of the catalytic unit (C) of the adenylate cyclase (as measured by forskolin stimulation), decreased monoexponentially however with a mol. wt. of 145 kDa. Both basal, DA- and flouride (F-) stimulated activity declined in a concave downward fashion with a limiting mol. wt. of 134, 138 and 228 kDa respectively. It was estimated that the basal and DA-stimulated activity originated from an enzyme complex with a mol. wt. of 325 kDa a value close to the combined size of RGS + C. These data suggest that F- stimulation of the adenylate cyclase, which occurs by a GS activation, does not cause disassociation of GS into the αS and βγ subunits. Further, the AA-regulated adenylate cyclase apparently exists as a complex consisting of RGS and C; the mechanisms of hormonal activation is dissociation of C from this complex