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SR Doctrow, SM Abelleira, LA Curry, R Heller-Harrison, JW Kozarich, B Malfroy, LA McCarroll, KG Morgan, AR Morrow and GF Musso
Alkermes, Inc., Cambridge, Massachusetts.
The vasoactive peptide bradykinin is believed to cause increased vascular permeability by the activation of B2 receptors on the vascular endothelium. A bradykinin analog, H-Arg-Pro-Hyp-Gly-Thi-Ser-Pro-4-Me- Tyr(psi CH2NH)-Arg-OH (RMP-7), was designed and it was proposed that it might increase cerebrovascular permeability by activating B2 receptors on brain microvasculature. In this report, the effects of RMP-7 and related peptides on bradykinin receptor-induced calcium signaling were examined in rat brain microvascular endothelial (RBME) cultures. RBME cells are responsive to bradykinin and exhibit specific [3H]-bradykinin binding, with Scatchard analysis indicating a major class of sites with a Kd of 3.9 +/- 1.4 nM and a minor class of higher affinity sites (Kd approximately 33 pM). RMP-7 displaces a significant component of specific [3H]-bradykinin binding from RBME cells; RMP-10, and RMP-7 diastereomer with a D-amino acid substitution in the number 9 position, does not. [3H]-bradykinin binding to RBME cells is not displaced by desArg9-bradykinin, which indicates that neither class of sites is a B1 bradykinin receptor. RMP-7 induces an increase in intracellular free calcium levels in RBME cells. The time course, magnitude and concentration dependence of RMP-7-induced calcium signaling is similar to that induced by bradykinin in RBME and other endothelial cells. Compared with RMP-7, RMP-10 is at least 1000 times less potent. However, the level of contamination by RMP-7 in the RMP-12 preparation accounts for its activity, an indication that both the RMP-10 and RMP- 12 diastereomers are essentially inactive.(ABSTRACT TRUNCATED AT 250 WORDS)
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