Heart rate modulates the slow enhancement of contraction due to sudden left ventricular dilation.
In isovolumic blood-perfused dog hearts, left ventricular developed pressure (DP) was recorded while a sudden ventricular dilation was promoted at three heart rate (HR) levels: low (L: 52 +/- 1.7 beats/min), intermediate (M: 82 +/- 2.2 beats/min), and high (H: 117 +/- 3.5 beats/min). DP increased instantaneously with chamber expansion (Delta(1)DP), and another continuous increase occurred for several minutes (Delta(2)DP). HR elevation did not alter Delta(1)DP (32.8 +/- 1.6, 33.6 +/- 1.5, and 34.3 +/- 1.2 mmHg for L, M, and H, respectively), even though it intensified Delta(2)DP (17.3 +/- 0.9, 20.7 +/- 1.0, and 26.8 +/- 1.2 mmHg for L, M, and H, respectively), meaning that the treppe phenomenon enhances the length dependence of the contraction component related to changes in intracellular Ca(2+) concentration. Frequency increments reduced the half time of the slow response (82 +/- 3.6, 67 +/- 2.6, and 53 +/- 2.0 s for L, M, and H, respectively), while the number of beats included in half time increased (72 +/- 2.9, 95 +/- 2.9, and 111 +/- 3.2 beats for L, M, and H, respectively). HR modulation of the slow response suggests that L-type Ca(2+) channel currents and/or the Na(+)/Ca(2+) exchanger plays a relevant role in the stretch-triggered Ca(2+) gain when HR increases in the canine heart.
Tucci
P J
PJ
Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, CEP 04023-900 São Paulo, Brazil. tucci@fcr.emp.br
Murad
N
N
Rossi
C L
CL
Nogueira
R J
RJ
Santana
O
O
D000818:Animals; D002404:Catheterization; D004285:Dogs; D006339:Heart Rate / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D016277:Ventricular Function, Left / Q000502:physiology*