Rate of onset of cardiotonic steroid-induced inotropism: influence of temperature and beat interval.

Isolated rabbit atria were employed to examine the rate of onset of inotropism of two glycosides (strophanthin and ouabain) and aglycones (acetylstrophanthidin and ouabagenin) under a variety of conditions of temperature and beat interval. The rate of onset of glycoside-induced inotropism was found to be highly and directly dependent on temperature between 27 and 37 degrees C at a beat interval of 10 seconds. At a beat interval of 1 second the rate of onset of glycoside effect was faster than at a beat interval of 10 seconds and was not dependent on temperature.

Effects of hemicholinium and bretylium on the release of autonomic transmitters in the isolated sino-atrial node.

1. In the isolated, spontaneously beating, sino-atrial node of the rabbit selective electrical excitation of intranodal autonomic nerve fibres results in a biphasic chronotropic response. This chronotropic response (negative followed by positive chronotropism) is due to the release of the autonomic transmitters (acetylcholine and noradrenaline, respectively) from intranodal nerve fibres.

Calcium movements across the membrane of human red cells.

1. A study has been made of the cellular content and movement of Ca across the membrane of human red blood cells.2.