High-affinity Neurotensin Receptor is Involved in Phosphoinositide Turnover Increase by Inhibition of Sodium Pump in Neonatal Rat Brain

Abstract

Phosphoinositide (PI) metabolism is enhanced in neonatal brain by activation of neurotransmitter receptors and by inhibition of the sodium pump with ouabain or endogenous inhibitor termed endobain E. Peptide neurotensin inhibits synaptosomal membrane Na(+), K(+)-ATPase activity, an effect blocked by SR 48692, a selective antagonist for high-affinity neurotensin receptor (NTS1). The purpose of this study was to evaluate potential participation of NTS1 receptor on PI hydrolysis enhancement by sodium pump inhibition. Cerebral cortex miniprisms from neonatal Wistar rats were preloaded with [(3)H]myoinositol in buffer during 60 min and further preincubated for 0 min or 30 min in the absence or presence of SR 48692. Then, ouabain or endobain E were added and incubation proceeded during 20 or 60 min. Reaction was stopped with chloroform/methanol and [(3)H]inositol-phosphates (IPs) accumulation was quantified in the water phase. After 60-min incubation with ouabain, IPs accumulation values reached roughly 500% or 860% in comparison with basal values (100%), if the preincubation was omitted or lasted 30 min, respectively. Values were reduced 50% in the presence of SR 48692. In 20-min incubation experiments, IPs accumulation by ouabain versus basal was 300% or 410% if preincubation was 0 min or 30 min, respectively, an effect blocked 23% or 32% with SR 48692. PI hydrolysis enhancement by endobain E was similarly blocked by SR 48692, being this effect higher when sample incubation with the endogenous inhibitor lasted 60 min versus 20 min. Present results indicate that PI hydrolysis increase by sodium pump inhibition with ouabain or endobain E is partially diminished by SR 48692. It is therefore suggested that NTS1 receptor may be involved in cell signaling system mediated by PI turnover.

Neurotensin decreases high affinity [3H]-ouabain binding to cerebral cortex membranes

“…Results showed that antagonist SR 48692 blocks the inhibitory effects of ouabain on sodium pump modulating phosphoinositide hydrolysis. This result suggests that high-affinity neurotensin receptors are involved, at least partially, in the process [36]. These findings may receive a new interpretation in the ligth of present results.…”

“…Herein we showed an interference between SR 48692 and ouabain at the Na + , K + -ATPase ouabain binding site. Therefore, it seems reasonable that the phosphoinositide hydrolysis increase by Na + , K + -ATPase inhibitors is prevented by in vitro addition of SR 48692 [36].…”

Na+/K+-pump and neurotransmitter membrane receptors

“…For example, neurotensin inhibits Na + /K + -ATPase activity of synaptosomal membranes from rat cerebral cortex (Lopez Ordieres and Rodriguez de Lores Arnaiz 2000). Neurotensin exerts these effects through activation of NTS1 receptors that results in PI hydrolysis (Pereyra-Alfonso et al 2008). In contrast, sub-µM angiotensin-(1-7) activates Na + /K + -ATPase from rat cerebral cortex synaptosomal membranes (Lopez Ordieres et al 1998).…”