Iron-56 irradiation diminishes muscarinic but not alpha 1-adrenergic-stimulated low-Km GTPase in rat brain.

Initial findings from our laboratory have indicated that muscarinic enhancement of K(+)-evoked release of dopamine from perifused striatal slices is reduced after exposure to 56Fe-particle irradiation. This finding suggested that there is a radiation-induced deficit in muscarinic receptor sensitivity. Subsequent findings have indicated that at least part of the loss in sensitivity may occur as a result of alterations in the initial steps of the signal transduction process and involve muscarinic receptor-G protein coupling/uncoupling. The present study was carried out to localize this deficit further by determining carbachol-stimulated low-Km guanosine triphosphatase (GTPase) activity in striatal and hippocampal tissue obtained from rats exposed to 0, 0.1 or 1.0 Gy of 56Fe-particle irradiation. In addition, to examine the specificity of the effect of 56Fe-particle irradiation, alpha 1-adrenergic-stimulated low-Km GTPase activity was also examined in these tissues. The results showed that there was a high degree of specificity in the effects of 56Fe particles. Decrements were observed in muscarinic-stimulated low-Km GTPase in striatum but not in hippocampus, and 56Fe-particle irradiation did not affect alpha 1-adrenergic low-Km GTPase activity in either brain tissue.