ECG alterations and microtubule proliferation following monocrotaline induced right ventricular heart failure in rats.
Institute of Membrane and Systems Biology,
*r.stones@leeds.ac.uk
Microtubules are load bearing and load-modulated components of the cardiac cytoskeleton whose proliferation may impede contractile function in animal and human right heart failure (Cooper, 2006) and possibly influence both mechano-electric feedback and excitation-contraction coupling. We wished to test whether there was a proliferation of microtubules in a non-invasive model of pulmonary hypertension induced by monocrotaline (MCT).
Male Wistar rats were injected with 60 mg/kg of MCT or an equivalent volume of saline (CON). Telemetry was used to measure the electrocardiogram (ECG) in vivo, in conscious, unrestrained animals on a weekly basis until day 21 then daily. On the presentation of clinical symptoms of heart failure (within 4 weeks), rats were killed, hearts removed and dissected into right ventricular (RV) and left ventricular (LV) portions and free and polymerised fractions of β-tubulin assessed using Western blot analysis. The mRNA expression ratio of α-tubulin was assessed in tissue samples from these regions using real-time reverse transcription polymerase chain reaction.
MCT treated rats had increased heart weight: body weight (CON 4.1 ± 0.2 vs. MCT 5.5 ± 0.2 mg/g) and RV weight:LV weight (CON 0.38 ± 0.03 vs. MCT 0.68 ± 0.06 g/g), consistent with the development of right ventricular hypertrophy/failure (n=6, CON and MCT t-test P=<0.001). Measurement of ECG parameters indicated modification of T-parameters in MCT treated animals including a prolonged QT interval (CON 49.7 ± 2.0 vs. MCT 76.2 ± 2.5 ms, P<0.001, t-test) and time from the peak to the end of the T-wave (Tpe, CON 25 ± 1.8 vs. MCT 33.1 ± 1.7 ms, P=0.007, t-test) (CON n=6, MCT n=7). In MCT treated rats there was an increase in the polymerised fraction of β-tubulin in the RV compared to control rats (CON 0.55 ± 0.02 vs. MCT 0.6 ± 0.01 a.u, P=0.003 2-WAY ANOVA, n=6 each group, 3 replicates). There was a concomitant increase the expression of mRNA encoding α-tubulin in the RV of MCT rats (CON 0.6 ± 0.1 n=7 vs. MCT 17.3 ± 4.2 a.u n=9, P<0.001, 2-WAY ANOVA).
We conclude that MCT treatment results in; ECG changes consistent with prolongation (QT) and increased global dispersion (Tpe) of the action potential duration; increased microtubule proliferation as evidenced by the increase in α-and β- tubulin. These changes may be relevant to alterations seen in the mechanical and electrical activity of right heart failure.
References
Cooper
G. Cytoskeletal networks and the
regulation of cardiac contractility: microtubules, hypertrophy, and cardiac
dysfunction. Am J Physiol Heart Circ Physiol 291, H1003-H1014, 2006.