CALCIUM MOVEMENTS DURING EXCITATION-CONTRACTION COUPLING IN MUSCLE-CELLS

Gross Ca exchange between the muscle cell and its environment is considered in various animals [frog, rat, guinea pig, monkey] in terms of the necessity for cellular free Ca regulation, both at rest and during the contraction-relaxation cycle. Methods of detecting cell Ca such as autoradiography, histochemistry involving oxalates and pyroantimonate, and X-ray microprobe analysis are discussed in relation to the elucidation of cell static Ca pools. The use of aequorin and intracellular scintillants are discussed as methods of tracing transient dynamic changes in cell Ca during activation and relaxation. The Ca uptake and release properties of sarcoplasmic reticulum, mitochondria and micropinocytotic vesicles are considered in terms of the cyclical modulation of cell Ca required during the EC [excitation-contraction] coupling cycle. The protein constituents of sarcoplasmic reticulum and mitochondria and cytoplasmic free proteins are considered in terms of their potential Ca binding properties in physiological conditions. The construction of these proteins into a workable model of a Ca pump/binding agency for cell Ca regulation is also considered.