Intracellular sodium determines frequency-dependent alterations in contractility in hypertrophied feline ventricular myocytes.
Am J Physiol Heart Circ Physiol
; 292(2): H1129-38, 2007 Feb.
Article
em En
| MEDLINE
| ID: mdl-17012360
ABSTRACT
Hypertrophy and failure (H/F) in humans and large mammals are characterized by a change from a positive developed force-frequency relationship (+FFR) in normal myocardium to a flattened or negative developed force-frequency relationship (-FFR) in disease. Altered Ca(2+) homeostasis underlies this process, but the role of intracellular Na(+) concentration ([Na(+)](i)) in H/F and frequency-dependent contractility reserve is unclear. We hypothesized that altered [Na(+)](i) is central to the -FFR response in H/F feline myocytes. Aortic constriction caused left ventricular hypertrophy (LVH). We found that as pacing rate was increased, contraction magnitude was maintained in isolated control myocytes (CM) but decreased in LVH myocytes (LVH-M). Quiescent LVH-M had higher [Na(+)](i) than CM (LVH-M 13.3 +/- 0.3 vs. CM 8.9 +/- 0.2 mmol/l; P < 0.001) with 0.5-Hz pacing (LVH-M 14.9 +/- 0.5 vs. CM 10.8 +/- 0.4 mmol/l; P < 0.001) but were not different at 2.5 Hz (17.0 +/- 0.7 vs. control 16.0 +/- 0.7 mmol/l; not significant). [Na(+)](i) was altered by patch pipette dialysis to define the effect of [Na(+)](i) on contraction magnitude and action potential (AP) wave shape at slow and fast pacing rates. Using AP clamp, we showed that LVH-M require increased [Na(+)](i) and long diastolic intervals to maintain normal shortening. Finally, we determined the voltage dependence of contraction for Ca(2+) current (I(Ca))-triggered and Na(+)/Ca(2+) exchanger-mediated contractions and showed that there is a greater [Na(+)](i) dependence of contractility in LVH-M. These data show that increased [Na(+)](i) is essential for maintaining contractility at slow heart rates but contributes to small contractions at fast rates unless rate-dependent AP shortening is prevented, suggesting that altered [Na(+)](i) regulation is a critical contributor to abnormal contractility in disease.
Buscar no Google
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Sódio
/
Hipertrofia Ventricular Esquerda
/
Miócitos Cardíacos
/
Contração Miocárdica
Tipo de estudo:
Prognostic_studies
Limite:
Animals
Idioma:
En
Revista:
Am J Physiol Heart Circ Physiol
Assunto da revista:
CARDIOLOGIA
/
FISIOLOGIA
Ano de publicação:
2007
Tipo de documento:
Article
País de afiliação:
Estados Unidos