No abstract

Extracellular and surface bound Ca is essential to excitation-contraction (E-C) coupling in mammalian cardiac muscle. In intact hearts from cardiomyopathic hamster with congestive heart failure, a concomitant decrease in the Ca content of a superficial pool was associated with the reduced contractility. Ca binding to cardiac sarcolemmal ghosts prepared from these hearts revealed two binding sites by Scatchard plot. In normal hamsters, the low affinity site had a capacity of 114 nmol Ca.mg-1 protein, a KD of 1.5 mmol . litre-1 and was sensitive to neuraminidase treatment but not to 100 mmol . litre-1 Na, K, or Li, Ca binding in vitro approached a 1:1 relationship with the sialic acid content of the ghosts, 159 nmol . mg-1 protein. The activity of the enzyme responsible for glycosidically linking sialic acid to interstitial and sarcolemmal glycoproteins, sialyltransferase, was reduced from 1.80 to 0.41 pmol . mg-1 protein in the myopathic hearts. We suggest the functional defect in the hamster cardiomyopathy is a reduction in sialyltransferase activity leading to the deficiency in surface sialic acid residues. As a consequence, contractility is reduced, but Ca influx is increased. Reflex sympathetic activity increases Ca influx resulting in "Ca overload" and eventual cellular necrosis.

No abstract

Reductions in cytochrome P-450 levels and aminopyrine N-demethylase activity of hepatic microsomes obtained from cardiomyopathic hamsters (BIO 14.6) occurred at all stages of the disease before the development of congestive heart failure (CHF). Cytochrome b5 levels were reduced only in animals with CHF when compared with age-matched controls (BIO.RB). Total microsomal protein and p-nitrophenol glucuronidation were not affected by the disease process. We conclude that the reduction in cytochrome P-450 levels and N-demethylase activity in cardiomyopathic hamsters is not a consequence of CHF, but is one of the manifestations of the disease process.