B2 bradykinin receptors in cultured neonatal rat cardiomyocytes mediate a negative chronotropic and negative inotropic response.
Receptors for bradykinin (BK) were characterized in primary cultures of beating neonatal rat cardiomyocytes using [3H]BK was radioligand. Degradation studies demonstrated that [3H]BK was stable for at least 2 h when incubated with cardiomyocytes at 2 and 37 degrees C in the presence of bacitracin in combination with captopril or ramiprilat. Without these inhibitors, > 80% of the [3H]BK was degraded within 2 h at 37 degrees C. This indicates that angiotensin-converting enzyme (ACE) is responsible for the main BK-degrading activity in cardiomyocytes. Scatchard plots were linear and gave a Kd of 1.5 +/- 0.8 nmol/l (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 degrees C led to internalization of the ligand. Competition studies with B1 and B2 agonists and antagonists were consistent with a B2 subtype of receptor. Addition of BK to beating cardiomyocytes (> 1 nmol/l) at 37 degrees C gave a strong but transient negative chronotropic effect. This response was paralleled by changes in the pulsation amplitude, which indicated 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 receptor-mediated mechanisms.
Medizinische Klinik I, Universität München, Germany.
A M
AM
Kasel
A
A
Faussner
A
A
Pfeifer
U
U
Müller
K
K
Werdan
A A
AA
Roscher
D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001414:Bacitracin / Q000494:pharmacology; D001920:Bradykinin / Q000378:metabolism; D002216:Captopril / Q000494:pharmacology; D002478:Cells, Cultured; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D018002:Receptors, Bradykinin / Q000502:physiology*
D000806:Angiotensin-Converting Enzyme Inhibitors; D018002:Receptors, Bradykinin; D001414:Bacitracin; D002216:Captopril; D001920:Bradykinin