Late ontogenetic development of adenosine A1 receptor coupling to associated G-proteins in guinea pig cerebellum but not forebrain

Abstract

The ontogenetic profile of [3H]forskolin and [3H]cyclohexyladenosine [( 3H]CHA) binding sites in guinea pig forebrain and cerebellum was investigated. G-protein interactions of these binding sites were also examined by analyzing 5'-guanylylimidodiphosphate (Gpp(NH)p) interactions with [3H]CHA and [3H]forskolin binding. In forebrain, similar binding characteristics of [3H]CHA and [3H]forskolin binding are observed between the developmental stages E36 (the earliest time point studied) through to adult (P28, the latest time point studied), although transient increased binding of both ligands is observed just prior to birth. Scatchard analysis of binding isotherms reveal that this transient rise just prior to birth is due to an increase in the number of binding sites (Bmax) with little or no change in receptor affinity (Kd). In contrast, in cerebellum both [3H]CHA and [3H]forskolin binding remains at a relatively low level until just prior to birth when a dramatic increase of binding of both ligands is observed which continues to increase up to P28. Scatchard analysis of binding isotherms reveal that such changes in binding of both ligands are largely due to increases in Bmax and not Kd, although Scatchard analysis of [3H]CHA binding to cerebellar E51 membranes reveals an absence of higher affinity [3H]CHA binding sites. Gpp(NH)p did not affect [3H]forskolin binding. Gpp (NH)p displacement profiles of [3H]CHA binding reveal a maximum (adult) inhibition of [3H]CHA binding (approximately 80% displacement) at all time points (E36 through P28) in forebrain membranes, but not in cerebellar membranes. In cerebellum, displacement of [3H]CHA binding by Gpp(NH)p is much greater after birth than before birth.(ABSTRACT TRUNCATED AT 250 WORDS)