3.2 Endogenous BK-(1-9) fragments induce NO production in vitro
To test whether BK-(1-9) fragments are biologically active, we tested
these BK fragments for their ability to induce NO production in
different cell types. We used cells from different species (i.e., human,
rat and mouse) and known to express the kinin B1 and
B2 receptors. As expected, incubation with BK-(1-9) (100
nM) increased NO production in immortalized human glioblastoma cells
(U-87 MG), neonatal male rat cardiomyocytes and male adult mouse
ventricular myocytes. BK-(1-9) fragments, BK-(1-7) and BK-(1-5), at the
same concentration, also induced NO production in these cell types
(Figure 2).
We then generated a concentration-response curve for NO production
mediated by BK-(1-9), BK-(1-7) and BK-(1-5) in neonatal male rat
cardiomyocytes. At all concentrations tested (1, 10, and 100 nM),
BK-(1-9) was able to elicit NO production (Figure 3A). The heptapeptide
fragment BK-(1-7) induced NO production in neonatal male rat
cardiomyocytes but only at the two higher concentrations (10 and 100 nM)
in a dose-dependent manner (Figure 3B). The pentapeptide metabolite
BK-(1-5) (Figure 3C) was able to induce NO production at all
concentration tested, including 1nM, but no significant difference was
observed between 10 and 100 nM. These results suggest that BK-(1-7) and
BK-(1-5) are not only metabolites of BK-(1-9) in vivo but, in vitro,
they were able to induce NO production in human and rodent cells.