Modulation of calcium sensitivity in cardiac muscle cells.

In the myocardium the relationship between intracellular free calcium and contraction is not unique but may vary over a wide range. Modulation of calcium sensitivity of the myofibrils may be studied in chemically skinned fibres which are devoid of the sarcoplasmic reticulum and in which the ionic composition of the interfilament space can be controlled and influenced at will. Here we review conditions and mechanisms which either lower or raise the free calcium ion concentration required for half maximal activation of a functionally isolated contractile mechanism.