Abstract
It is well known that in the cardiac muscle the amount of uptake of Ca ions depends on external Ca concentration and on the electrically driven rate of the preparation (1-5). These Ca ions taken up are considered to play an important role as a direct or indirect activator of the contractile system of the muscle (6, 7).
According to Lüttgau and Niedergerke (8) and Niedergerke (2, 3), the external Ca ions may be carried into the heart cells in combination with a hypothetical receptor site or molecule, R. This RCa complex, which may be in close equilibrium with external Ca concentration, appears to move inward, when the membrane is depolarized, so as to initiate the contraction.
In the present report, the relationship between external Ca concentration and contractile force in guinea-pig atria driven electrically was analyzed with the formulation of the above scheme in the kinetic equations originated by Michaelis and Menten (9).
Furthermore, the mode of the modification of the above relationship by Mn ions was analyzed in terms of the same kinetic models.
