PT  - JOURNAL ARTICLE
AU  - M K Park
AU  - F F Vincenzi
TI  - Influence of calcium concentration on the rate of onset of cardiac glycoside and aglycone inotropism.
DP  - 1976 Sep 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 680--686
VI  - 198
IP  - 3
4099  - http://jpet.aspetjournals.org/content/198/3/680.short
4100  - http://jpet.aspetjournals.org/content/198/3/680.full
SO  - J Pharmacol Exp Ther1976 Sep 01; 198
AB  - Isolated rabbit atria were employed to examine the rate of onset of inotropism of two glycosides (strophanthin and ouabain) and aglycones (acetylstrophanthidin and ouabagenin) in the presence of various concentrations of calcium (0.55, 1.1, 2.2, 4.4 and 8.8 mM). The rate of onset of glycoside-induced inotropism was found to be greatly influenced by the calcium concentration. The rate of onset was increased in both low and high calcium, with the minimum rate of onset at 1.1 or 2.2 mM calcium. In contrast, the rate of onset of aglycone-induced inotropism was not dependent on calcium between 0.55 and 4.4 mM calcium. The rate of onset of aglycone-induced inotropism was increased at 8.8 mM calcium. The results are interpreted by postulating that the digitalis inotropic receptor is located in a membrane-limited compartment to which aglycones may gain access via passive diffusion but to which glycosides gain access mainly via a (calcium-dependent) carrier mechanism.