This is a study of the myocardial sarcolemma. Its approach is to analyze the ultrastructure of the glycocalyx and the bilayer with cytochemical and freeze-fracture techniques.
The specific aims are to determine, 1) if the glycocalyx and the intramembrane particles (IMP's) in the bilayer are related to membrane permeability, and 2) how these components of the membrane are related to each other. The methodology is to examine their morphology after perturbations which alters membrane permeability or transport, during maturation of the sarcolemma, within specializations of the sarcolemma and after alterations in the anionic phospholipids within the bilayer. Structural changes in the IMP's and the cell surface will be related to the onset, to the degree and to the prevention of altered membrane function. To this end the following perturbations will be used: 1) Ca depletion and repletion, 2) ischemia, 3) digitalis toxicity, 4) phospholipase D treatment and exposure to amphiphiles. The developmental studies will compare the structure of the sarcolemmal components in the neonate and adult hearts. Investigation of the relationship between the glycocalyx and IMP's will involve induction of clustering of the IMP's and determining if there is a parallel distribution of cell surface cytochemical markers. In reverse, cell surface components (cationized ferritin and Con A receptors) will be capped and the fractured sarcolemma monitored for a parallel distribution of IMP's. Conventional freeze-fracturing techniques plus refinements such as ultra-rapid freezing, rotary shadowing will be used to describe and quantify IMP's (number, distribution, size, substructure). Thin-section microscopy will use colloidal iron hydroxide, cationized ferritin, Con A and tannic acid fixation. The proposed research has a two-fold significance: 1) by testing whether the glycocalyx and IMP's are related to permeability of the membrane it addresses a question fundamental to the biology of all cells, and 2) it focuses on the structure-function relationships (physiological and pathophysiological) of the """"""""greater membrane,"""""""" where in the heart there is little information, using state of the art techniques.
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