The bradykinin analog RMP-7 increases intracellular free calcium levels in rat brain microvascular endothelial cells.

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)