DIABETES, VOLUME 45, SUPPLEMENT 1, JANUARY 1996, PAGES S44-S50

B₂ Bradykinin Receptors in Cultured Neonatal Rat Cardiomyocytes Mediate a Negative Chronotropic and Negative Inotropic Response

Albert M. Kasel, Alexander FauBner, Alexander Pfeifer, Ursula Muller, Karl Werdan, and Adelbert A. Roscher

Receptors for bradykinin (BK) were characterized in primary cultures of beating neonatal rat cardiomyocytes using [³H]BK as radioligand. Degradation studies demon-strated that [³H]BK was stable for at least 2 h when incubated with cardiomyocytes at 2 and 37°C in the presence of bacitracin in combination with captopril or ramiprilat. Without these inhibitors, >80% of the [ H]BK was degraded within 2 h at 37°C. This indicates that angiotensin-converting enzyme (ACE) is responsible for the main BK-degrading activity in cardiomyocytes. Scat-chard plots were linear and gave a K_d of 1.5 + 0.8 nmol/1 (mean + SD, n = 4) and a maximum binding capacity of 55-125 fmol/mg protein. Association and dissociation studies showed that binding of [³H]BK was saturable and reversible. Binding of [³H]BK at 37°C led to internaliza-tion of the ligand. Competition studies with B₁ and B₂ agonists and antagonists were consistent with a B₂ sub-type of receptor. Addition of BK to beating cardiomyo-cytes (>1 nmol/1) at 37°C gave a strong but transient negative chronotropic effect. This response was paral-leled by changes in the pulsation amplitude, which indi-cated a simultaneous negative inotropic effect of BK. These results provide a basis for the hypothesis that ACE inhibition exerts its cardioprotective effect at the level of a population of cardiomyocytes by virtue of kinin recep-tor-mediated mechanisms. Diabetes 45 (Suppl. 1):S44--S50, 1996

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