Surface Calcium in the Heart: Its Function and Role in Drug Action
It is well documented that activation of the myofilaments in striated muscle is controlled by an increase in calcium (Ca2+) delivery to troponin sites on the myofilaments (Solaro et al., 1974; Ebashi, 1963). Calcium ions enter the cytoplasm from surface membrane sites and intracellular storage sites in response to membrane depolarization. In skeletal muscle the Ca2+ involved in the E-C coupling process is released and sequestered entirely intracellularly (Armstrong et al., 1972; Winegrad, 1970). Cellular Ca2+ exchanges in skeletal muscle at a slow rate and reacts slowly to alterations of the external Ca2+ concentration (Rich and Langer, 1975; Lüllmann et al., 1974). When a skeletal muscle is perfused with a Ca2+-free medium the decline of tension has a T1/2 of 23 min (Fig. 1). The large lateral sacs of the sarcoplasmic reticulum serve in skeletal muscle as storage and release sites for activator Ca2+ (Endo and Nakajima, 1973; Winegrad, 1968).
KeywordsSialic Acid Surface Coat Sialic Acid Residue Cell Coat Colloidal Iron
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