Tachykinin Receptors of the NK1 Type (Substance P) Coupled Positively to Phospholipase C on Cortical Astrocytes from the Newborn Mouse in Primary Culture

Specific 125I-Bolton-Hunter substance P (125I-BHSP) binding sites are present on intact cortical astrocytes of the newborn mouse in primary culture. Therefore, these cells were used to ascertain the existence of functional substance P (SP) receptors coupled positively to phospholipase C. SP stimulated phosphoinositide breakdown with an EC50 value (4.5 x 10(-10) M) similar to its IC50 value (3.8 x 10(-10) M) for inhibiting 125I-BHSP binding. The maximal response to (10(-6) M SP for 60 min) obtained was approximately 500% of control values. The rank order of potency of tachykinins was SP greater than neurokinin (NK) A greater than NKB. Long SP C-terminal fragments were more potent than shorter ones in stimulating the accumulation of 3H-inositol phosphates. SP free acid and SP N-terminal fragments were without effect. [L-Pro9]SP and SP methyl ester, two selective agonists of NK1 receptors, were almost as potent as SP. An excellent correlation was found when the abilities of tachykinins and their analogs for stimulating phosphoinositide breakdown and for inhibiting 125I-BHSP binding were compared. Finally, when used at a concentration of 3 x 10(-6) M, spantide [( D-Arg1, D-Trp7,9, Leu11]SP), an SP antagonist, competitively reduced the stimulatory effect of SP on accumulation of 3H-inositol phosphates. These results demonstrate the presence of functional SP receptors (NK1) on cortical astrocytes from the newborn mouse in primary culture.