Myosin isoenzyme distribution in overloaded human atrial tissue.

Abstract

Using nondenaturing polyacrylamide gel electrophoresis, we have identified two distinct myosin isoenzymes in human atrial tissue that correspond to the V1 and V3 isomyosins found in rat ventricular tissue. Normal left and right atrial appendages have approximately 50% V3. When the left atrium was exposed to hemodynamic overload secondary to mitral stenosis, the percent V3 increased to 77 + 10% (n = 10); exposure to hemodynamic overload secondary to mitral regurgitation caused an increase to 70 14% (n = 6). Changes in the isoenzyme pattern were seen in the right atria of patients with mitral stenosis and markedly elevated pulmonary arterial pressures compared with control subjects and patients with mitral stenosis without severe pulmonary hypertension. Several clinical variables were examined to determine which factors might influence isoenzyme expression. Age, sex, the presence of atrial fibrillation, and pulmonary capillary wedge pressure did not predict the isoenzyme pattern. However, patients with mitral valvular disease and only slightly enlarged left atria tended to have a higher percent V3 than those with massively enlarged atria. These data confirm that human atrial tissue, like rat ventricular tissue, can alter its isomyosin composition in response to a hemodynamic load. The data further suggest that the isoenzyme shift is an early adaptation to the imposed load. Circulation 74, No. 3, 477-483, 1986. EXPERIMENTAL STUDIES in many mammalian species have demonstrated that the biochemical constituents of the myocardium, especially the heavy chains of myosin, influence the mechanical performance of cardiac muscle1' 2 and that changes in expression of the various isomyosins mediate myocardial adaptations to imposed loads and/or hormonal stimuli.3'4 This is particularly apparent in rodents and other small animals. Several investigators have shown, for example, that the imposition of hypertension or aortic stenosis on rat ventricle shifts the normally V1 predominant isomyosin to V3, which is associated with reduced ATPase activity and with depressed mechanical properties. Conversely, the superimposition of physical training or hyperthyroidism increases the percentage of V1, the associated ATPase activities, and the velocity of contraction of the intact muscle.3 5-In human ventricular tissue, which is composed almost exclusively of an isomyosin homodimer with a From

Atrial contractile protein content and function are preserved in patients with coronary artery disease and atrial fibrillation

“…Here in patients with normal ventricular function, we showed no change in myosin isoform composition in patients with AF in comparison with the NSR group. These results are in agreement with Buttrick et al [18] but differ from the results of Narolska et al [19] where an increase in the percent composition of the b-myosin heavy chain in the AF group was reported. Increases in human atrial b-myosin heavy chain expression have been associated with the hemodynamic stress of mitral valve disease and ventricular dysfunction [9,18,20] and thus may be a factor in these previously reported shifts in myosin isoform expression.…”

“…These results are in agreement with Buttrick et al [18] but differ from the results of Narolska et al [19] where an increase in the percent composition of the b-myosin heavy chain in the AF group was reported. Increases in human atrial b-myosin heavy chain expression have been associated with the hemodynamic stress of mitral valve disease and ventricular dysfunction [9,18,20] and thus may be a factor in these previously reported shifts in myosin isoform expression. In addition, posttranslational changes in myosin can also affect its function and have been implicated as contributors to the contractile deficit in human, and animal models of myocardial failure.…”

“…In addition, posttranslational changes in myosin can also affect its function and have been implicated as contributors to the contractile deficit in human, and animal models of myocardial failure. These include oxidative stress injury, light chain phosphorylation, proteolytic degradation, and shifts in light chain isoform expression [16,18,[21][22][23][24][25]. Here we show that the contractile function of myosin is preserved in human AF, and thus if any compositional change in myosin is present, it is likely small, so as to not affect mechanical function.…”

Sex differences in myosin heavy chain isoforms of human failing and nonfailing atria

“…Buttrick et al (6) reported that there is an increase in the relative amount of the native myosin, V3, which has the MHC-␤ isoform, in the left atrium in association with mitral stenosis. It is possible, therefore, that the higher level of MHC-␤ in women than in men is associated with the greater occurrence of mitral valve stenosis in women, although there is insufficient information to evaluate the extent of stenosis among subjects in the present study and its contribution to the observations.…”

Single nucleotide polymorphisms, haplotypes and combined genotypes in MYH3 gene and their associations with growth and carcass traits in Qinchuan cattle

“…During the development and the adult, α - MYH is predominately expressed in the atrial chamber and β - MYH in the ventricular chamber in both humans and chicks [29–33]. This is further illustrated by the increased expression of β - MHC in the atria of human hearts under pressure overload [34, 35]. MHC analysis of human soleus muscle shows that this muscle expresses an approximately equal mix of type I and IIa isoforms, but the type IIx MHC is not expressed [36].…”