Zur Frage der herzwirksamen Form des Kalkes

Importance of Calcium in the Actions of Some Drugs That Stimulate the Isolated Hypodynamic Frog Heart

“…It is therefore suggested that the prime action of cardiacglycosides is to increase the superficial pool of calcium required for the propagation of the excitatory process from the cell membrane inwards; but, if so, at least some of the calcium may come from stores of calcium already present in the heart, since the distinguishing feature of the action of the glycosides is their ability to cause stimulation in calcium-free Ringer when the heart store of calcium is not depleted. This view has something in common with that of Pohle (1935), who believed that strophanthus caused shifts in the equilibrium between ionic calcium, calcium complexes and protein-bound calcium complexes in the heart. In addition, however, ouabain can probably facilitate the uptake of calcium from the perfusing fluid, since though it cannot stimulate hearts in which calcium stores are depleted yet the contractile response returns relatively rapidly when perfusion with low-calcium Ringer is resumed.…”

“…Calcium is believed to be present in the heart partly in the ionic form, but largely in some form of chemical combination (Pohle, 1935;Krogh, Lindberg & SchmidtNielson, 1944). Hajdu & Leonard (1959) suggest that calcium is involved in a normal muscle twitch response in at least three sites-at the cell membrane, which is, however, very resistant to calcium deprivation; at a superficial site where it is required for the propagation of excitation from the cell membrane inwards; and, finally, at the contractile protein itself which requires calcium in order to contract.…”