title: Dependence of the cardiac uptake of digitalis glycosides on the extracellular calcium concentration in guinea pig isolated hearts.
abstract: The purpose of the present study was to investigate, at the myocardial level, the divergent influences of Ca2+ on the action of various cardiotonic steroids. Therefore, the cardiac uptake of 3-H-digitoxin and 3-H-digitoxin was studied in experiments on guinea pig isolated hearts. The following results were obtained: with digitoxin the increase of the extracellular calcium concentration from 0.45 upto 7.2 mM resulted in a concomitant decrease of the myocardial glycoside uptake from about 1.8 nmoles/g wet weight down to about 1.2 nmoles/g wet weight. Similar results were obtained when digoxin uptake was studied under the same conditions: with 0.45 mM Ca2+ about 0.6 nmoles/g wet weight were bound, increasing the calcium concentration upto 7.2 mM lead to a concomitant decrease of the cardiac digoxin uptake down to about 0.45 nmoles/g wet weight. Despite the different physicochemical behaviour of these two drugs and the different amounts of drug present in the hearts the influence of Ca2+ was almost identical if calculated on a relative basis. So far, no experimental based explanation can be given for the above discrepancies. Other possible interpretations are discussed.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004074:Digitoxin / Q000378:metabolism*; D004077:Digoxin / Q000378:metabolism*; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D005630:Fructans; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion
chemical_list: D005630:Fructans; D009124:Muscle Proteins; D004077:Digoxin; D004074:Digitoxin; D002118:Calcium