PROPERTIES AND FUNCTIONS OF A NEUROMEDIN-B-PREFERRING BOMBESIN RECEPTOR IN BRAIN MICROVASCULAR ENDOTHELIAL-CELLS

Endothelial cells were isolated from rat brain microvessels and grown in vitro. They expressed a high density of [I-125-Tyr4]bombesin recept ors (B-max = 0.9 pmol/mg protein) with an apparent K-d value of 10 nM. The pharmacological profile of inhibition of the specific [I-125-Tyr4 ]bombesin binding [bombesin = neuromedin B > gastrin releasing peptide (GRP)] was consistent with the presence of a neuromedin-B-preferring receptor. Addition of bombesin, neuromedin B and GRP increased the act ivity of phospholipase C as measured by the production of total inosit ol phosphates and from intracellular Ca2+ measurements. They increase Rb-86(+) uptake by the Na+, K+, 2Cl(-) cotransporter and by a charybdo toxin-sensitive, Ca2+-activated K+ channel and Na-22(+) uptake by the Na+/H+ exchanger. The pharmacological profiles of activation of phosph olipase C, Na+ K+, 2Cl(-) cotransport and Na+/H+ exchange by bombesin- like peptide were consistent with an involvement of the neuromedin-B-p referring receptor characterized in binding experiments. It is suggest ed that one of the actions of neuromedin B in brain vessels could be t o control K+ secretion by the blood/brain barrier.