Effect of pyruvate on the dependence of electromechanical activity on stimulation frequency in human myocardium

Vida Gendvilienė¹, Danguolė Zablockaitė¹, Agnė Babušytė¹, Jonas Jurevičius¹, Rimantas Benetis^{1, 2}

¹Institute of Cardiology, Kaunas University of Medicine, ²Clinic of Cardiac Surgery, Kaunas University of Medicine Hospital, Lithuania

Key words: human myocardium, stimulation frequency, pyruvate, contraction force, relaxation time, action potentials.

Summary. The aim of the study was to determine the effect of pyruvate, a substrate of energetic metabolism, on the dependence of electromechanical activity on stimulation frequency in human myocardium.

The experiments were performed on human ventricle myocardium from patients undergoing cardiac corrective open heart surgery at Clinic of Cardiac Surgery in Kaunas University of Medicine by using standard method of registration of myocardium electromechanical activity. The stimulation frequency of myocardial strips were 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 and 3 Hz, duration of pulses –2–5 ms. In control, i.e. at perfusion of mycoardial strips by Tyrode solution and stimulation frequency 1 Hz, an average of contraction force (P) was 0.94±0.18 mN (n=12), half time of relaxation (t_a) – 178.88±9.31 ms (n=12), and action potential duration measured at 50% repolarization level (VP₅₀) – 294.75±27.95 ms (n=9). Pyruvate (10 mM) increased P to 159.9±13.4% (p<0.00), t_a – 106.9±2.2% (n=12) (p<0.001), and VP₅₀ – 111.1±7.4% (n=5) (p<0.05), as compared to control.

In the absence of pyruvate values of P, t_a and VP₅₀ of myocardial strips were higher at 0.2 Hz and 0.5 Hz and lower at 3 Hz compared with those at 1 Hz of stimulation frequency. Although the dependence of these parameters on stimulation frequency in the presence of pyruvate (10 mM) was not altered but their values were persistently increased at all stimulation frequencies. The present data indicate that pyruvate is an effective inotropic agent, which can improve contractility function in wide-ranging diapason of stimulation frequency in failing human heart.

Correspondence to V. Gendvilienė, Institute of Cardiology, Kaunas University of Medicine, Sukilėlių 17, LT-50009 Kaunas, Lithuania. E-mail: membiof@kmu.lt

Received 14 May 2004, accepted 1 October 2004