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The myosin light chain complement and proteolytic peptide patterns of myosin heavy chains were studied by two-dimensional and one-dimensional electrophoretic techniques respectively, in a total of 57 samples from ventricular and atrial tissues of normal and hypertrophied human hearts. Hypertrophies were classified haemodynamically as due to pressure-overload and volume-overload. In addition to the occurrence of ventricular light chains in hypertrophied atria we also observed the atrial light chain-1 (ALC-1) in hypertrophied ventricular tissues. On average over 6% of total light-chain-1 comprised ALC-1 in pressure-overloaded ventricles and around 3% in volume-overloaded ventricles. In single cases of pressure-overload ALC-1 amounted up to over 20% of total light chain-1. With regard to the myosin heavy chains limited digestion by two different proteinases produced over 200 clearly resoluble peptides. The absence of any detectable differences in the peptide patterns between myosin heavy chains from normal and hypertrophic tissues of left or right ventricle is in line with the findings of J. J. Schier and R. S. Adelstein (J Clin Invest 1982; 69: 816-825). In atrial tissues however, reproducible qualitative differences in the peptide patterns indicated that during hypertrophy a different type of myosin heavy chains becomes expressed. No differences were seen between the myosin heavy chains from normal left and right atria.

Dispersed bovine parathyroid cells were incubated in vitro with 3H-labeled amino acids for 30--120 min. Analysis of cell extracts by sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis revealed a calcium-regulated incorporation of 3H-labeled amino acids into three major peaks, one with a molecular weight (Mr) of 70,000 and two peaks in the 10,000 Mr region, and a minor 5,000 Mr peak. Furthermore, [3H]mannose was incorporated into the 70,000 Mr peak, which corresponds to the parathyroid secretory protein (PSP) recognized as a glycoprotein. The two peaks in the 10,000 Mr region had the electrophoretic mobility of [3H]bovine proparathyroid hormone (ProPTH) and [3H]bovine PTH (1--84), respectively. Immunoreactive PTH was only detected in a peak comigrating with [3H]PTH-(1--84). The nonimmunoreactive 5,000 Mr peptide was not further identified. The incorporation of radioactive amino acids into PSP, ProPTH, PTH-(1--84), and the 5000-daltons peptide was inversely related to the calcium concentration in the incubation medium. The incorporation of radioactive mannose into PSP was also greater at low extracellular calcium concentrations. Our findings provide evidence for an inverse relationship between the extracellular calcium concentration and the formation of PSP, ProPTH, PTH-(1--84), and a yet to be identified 5000-dalton peptide in dispersed bovine parathyroid cells.

The light chains of myosin from atrial and ventricular tissues from rat and rabbit were examined by one- and two-dimensional polyacrylamide gel electrophoresis. The myosin heavy chains were electrophoretically isolated, digested after denaturation in sodium dodecyl sulfate with papain and proteinase from S. aureus V8, and the resulting peptides resolved in one-dimensional gel electrophoresis. The peptide patterns of myosin heavy chains from atrial and ventricular tissues of adult rabbits were different, indicating differences in their primary structures. No such differences could be detected in a total of around 180 peptides produced by the two proteinases from the myosin heavy chains of adult rat atrial and ventricular tissues. With regard to light chains, the same migration pattern was observed for atrial and ventricular tissues from both rat and rabbit. The atrial light chains ALC1 and ALC2 migrated with molecular weights lying between those of the ventricular light chains VLC1 and VLC2. In two-dimensional electrophoresis, the corresponding light chains from rat and rabbit co-migrated. An additional light chain was observed in foetal ventricles, which exhibited identical electrophoretic properties to ALC1 from adult atrial tissues. In rat myofibrillar preparations from atrium and ventricle, an unidentified protein (x) occurred in the region of light chain-1 but with a more acidic isoelectric point, which seems to be related to the developmental stage of these tissues and which could not be detected in rabbit heart tissues or in any skeletal muscles.

Hemodynamic and angiographic parameters, muscle fiber diameter, nonmuscle tissue content, and myosin light chain isoform composition were determined in the left ventricle of nine patients with primary (four with hypertrophic, five with dilated cardiomyopathy) and 27 patients with secondary hypertrophy (11 with aortic regurgitation, 16 with aortic stenosis), nine patients with coronary heart disease, and seven controls. In various forms of hypertrophy, a new atrial-like light chain 1 occurred in two-dimensional electrophoresis of total tissue homogenates amounting up to 29% of total light chain 1. Total light chain 1 content remained constant in all groups when related to tropomyosin. The mean content of this atrial light chain 1 was highest in dilated cardiomyopathy (12.1%), less in cases with pressure (6.4%) and volume overload (2.9%), but as low in hypertrophic cardiomyopathy (0.3%) as in controls (0.4%). In cases with coronary heart disease without prior infarction, it was lower (0.6%) than with infarction (1.9%). Its occurrence was not affected by digoxin administration. In ventricular myocardium, an atrial-like light chain 2 was never observed. Peptide patterns after limited proteolytic digestion of isolated myosin heavy chains from cases with pressure overload and hypertrophic cardiomyopathy were identical to those from controls. The content of the atrial-like light chain 1 was not correlated to either muscle fiber diameter or nonmuscle tissue content, both of which were increased in all hypertrophy groups. In individual cases, no firm correlation could be established between atrial-like light chain 1 content and various parameters of ventricular load and function. However, a significant correlation resulted when the mean values of atrial-like light chain 1 content of each disease group were related to the respective mean values of peak circumferential wall stress (r = 0.96). Thus, the shift of myosin light chain 1 isoforms in ventricle seems to characterize biochemically the hypertrophy process induced by mechanical stress.

1. Rabbit cardiac myosins from atrium and ventricle were found to differ in their native form in pyrophosphate gel electrophoresis as well as in their light chain pattern in one- and two-dimensional electrophoretic systems. 2. The myosin light chain pattern in sodium dodecylsulfate gel electrophoresis differs between atrial and ventricular tissues in the mammalians (rabbit, dog, human, pig, sheep and rat) but not in the chicken. 3. In foetal rabbit ventricle an additional light chain is observed which, in two-dimensional electrophoresis with adult cardiac light chains, was found to be the same as atrial light chain-1.