Involvement of sulfhydryl groups in cerebral cortical [ 3H]clonidine binding in developing rats

Abstract

The involvement of essential sulfhydryl groups in α 2-adrenoceptor function was investigated in the cerebral cortex of 7 and 70 day old rats. N-Ethylmaleimide (NEM) inhibited specific [ 3H]clonidine binding to cerebral cortical membranes in a concentration-dependent and biphasic manner in both infant and adult rats. The inhibitory effect of NEM was attenuated by simultaneous addition of dithiothreitol 30 μM and 1 nM, though dithiothreitol up to 1 nM did not affect the binding. p-Chloromercuriphenylsulfonic acid also caused a significant reduction in [ 3H]clonidine binding at both stages. Scatchard analysis of [ 3H]clonidine binding showed that NEM 10 and 100 μM caused a significant decrease in Bmax of high affinity binding sites without changing K D. Neither Bmax nor K D values were changed by NEM 10 and 100 μM in low affinity sites. The treatment with NEM 10 and 100 μM significantly reduced the increase of binding induced by Mn 2+ 10 and 100 μM which was observed on day 70 but not on day 7. It is suggested that two distinct categories of essential sulfhydryl groups are involved in cerebral cortical α 2-adrenoceptors and are functionally mature by day 7. Furthermore, sulfhydryl groups are involved in the Mn 2+-induced increase of α 2-receptors in adult rats.