DISTRIBUTION OF MUCOSUBSTANCES IN THE DEVELOPING RAT HEART
ROGER R. MARKWALD 1 and
WILLIAM N. ADAMS SMITH 1
1 Department of Anatomy, Medical University of South Carolina, Charleston, South Carolina 29401
Mucosubstances (MS) were examined in 10
-14
-day embryonic rat hearts utilizing nonaqueous fixatives or formaldehyde vapor-fixed frozen sections hydrated in concentrated solutions of cetylpyridinium chloride. Ribonuclease-resistant, polyanionic sites were limited to the extracellular cardiac jelly, endocardium and fibroblastic cells (cushion tissue) associated with the endocardium. The cardiac jelly and endocardium of day 10
embryos principally contained a hyaluronic acid-like carboxylated mucosubstance whose alcianophilia at pH 2.5 was abolished by hyaluronidase but was resistant to NaOH extraction and neuraminidase and trypsin digestion. A critical electrolyte concentration of 0.2 M MgCl2 abolished alcianophilia. On days 13
-14
carboxylated MS were restricted to cushion tissue and partially resisted mild methylation. Sulfated MS were limited to primitive endocardial cells which gave origin to cushion tissue. Dye deposits of aldehyde fuchsin, high iron diamine or Alcian Blue (pH 1.0) were localized on cell surfaces and such staining was prevented by strong (60°C) methylation. Hyaluronidase sensitivity of sulfated MS decreased with gestation. The critical electrolyte concentration varied from 0.5-0.7 M MgCl2 on days 11
-12
to 0.8-0.9 M MgCl2 after day 12
. The sulfated MS of endocardial cells were preceded by a transitory accumulation of diastase-resistant, periodic acid-Schiff-positive material. Possible roles of MS in normal and abnormal cardiac septation processes are discussed.
Submitted on November 10, 1971