Viral-mediated overexpression of Rrm1+Rrm2 in adult rat cardiomyocytes increased the extent of shortening by ~40%, maximal rate of shortening by ~80%, and maximal rate of relaxation by ~150%.
Does viral-mediated overexpression of Rrm1 and Rrm2 improve contractility and relaxation in adult rat cardiomyocytes?
Overexpression of ribonucleotide reductase increases intracellular dATP and enhances cardiomyocyte contractility and relaxation without altering calcium handling.
We have previously demonstrated that substitution of ATP with 2 deoxy-ATP (dATP) increased the magnitude and rate of force production at all levels of Ca(2+)-mediated activation in demembranated cardiac muscle. In the current study we hypothesized that cellular dATP could be increased by viral-mediated overexpression of the ribonucleotide reductase (Rrm1 and Rrm2) complex, which would increase contractility of adult rat cardiomyocytes. Cell length and ratiometric (Fura2) Ca(2+) fluorescence were monitored by video microscopy. At 0.5Hz stimulation, the extent of shortening was increased ~40% and maximal rate of shortening was increased ~80% in cardiomyocytes overexpressing Rrm1+Rrm2 as compared to non-transduced cardiomyocytes. The maximal rate of relaxation was also increased ~150% with Rrm1+Rrm2 overexpression, resulting in decreased time to 50% relaxation over non-transduced cardiomyocytes. These differences were even more dramatic when compared to cardiomyocytes expressing GFP-only. Interestingly, Rrm1+Rrm2 overexpression had no effect on minimal or maximal intracellular Ca(2+), indicating increased contractility is primarily due to increased myofilament activity without altering Ca(2+) release from the sarcoplasmic reticulum. Additionally, functional potentiation was maintained with Rrm1+Rrm2 overexpression as stimulation frequency was increased (1Hz and 2Hz). HPLC analysis indicated cellular dATP was increased by approximately 10-fold following transduction, becoming ~1.5% of the adenine nucleotide pool. Furthermore, 2% dATP was sufficient to significantly increase crossbridge binding and contractile force during sub-maximal Ca(2+) activation in demembranated cardiac muscle. These experiments demonstrate the feasibility of directly targeting the actin-myosin chemomechanical crossbridge cycle to enhance cardiac contractility and relaxation without affecting minimal or maximal Ca(2+). This article is part of a Special issue entitled "Possible Editorial".
Korte et al. (Wed,) reported a other. Viral-mediated overexpression of Rrm1+Rrm2 vs. Non-transduced cardiomyocytes was evaluated on Extent of shortening, maximal rate of shortening, and maximal rate of relaxation. Viral-mediated overexpression of Rrm1+Rrm2 in adult rat cardiomyocytes increased the extent of shortening by ~40%, maximal rate of shortening by ~80%, and maximal rate of relaxation by ~150%.
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