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Actomyosin, Collagen, and Succinate Dehydrogenase Determinations in Opossum Esophageal Muscles

The contractile activities of the lower esophageal sphincter (LES), esophageal body smooth muscle (SM), and esophageal body striated muscle (ST) of the opossum differ in their dependence on oxygen. One possible explanation for this difference in oxygen dependence is that the muscles differ in their oxidative capacities. The purpose of this study was to estimate the oxidative. capacity of these muscles by measuring the activity of succinate dehydrogenase (SDH). Since the muscles are structurally as well as functionally distinct, we also determined the amount of actin, myosin, collagen, and total protein in the tissues. LES contained less total protein and more collagen than SM and ST. The actin contents per unit of total protein of all three tissues were similar. The myosin contents and the actin: myosin ratios, however, were significantly different among all three muscles. The interpretation of the values of the SDH activity depended on the manner in which the data were expressed. When SDH activity was expressed relative to the tissue content of myosin, the values were different among all three muscles. These findings support the hypothesis that there is biochemical variability in these three esophageal muscles that may account in, part for their differences in contractile behavior.