Inhibition of erythrocyte Ca2(+)-pump by Ca2+ antagonists.
Inside-out vesicularized membrane fragments from human erythrocytes were prepared to study the effects of various Ca2+ channel entry blockers of plasma membrane Ca2+ transport and (Ca2+ + Mg2+)-ATPase activity concomitantly. Verapamil and diltiazem (0.01 to 5 mM) inhibited both (Ca2+ + Mg2+)-ATPase activity and initial rates of 45Ca2+ net uptake analogously. In general, the parameter affected most by these drugs, using either Ca2+ transport or (Ca2+ + Mg2+)-5'-adenosine-triphospho-hydrolase (EC 3.6.1.3) ([Ca2+ + Mg2+]-ATPase) measurements, was the stimulation by calmodulin. However, the specificity and selectivity of inhibition appeared to be highly concentration and membrane preparation dependent. Verapamil and diltiazem inhibited the calmodulin-Ca2+ transport concentration-effect relationship by changing its apparent affinity as well as the maximal velocity of the process. In a "white ghost" membrane preparation, bepridil inhibited calmodulin activation with a high degree of selectivity as opposed to its effects on calmodulin activation in the vesicular preparation. Nifedipine failed to exhibit any specificity and modestly inhibited basal and calmodulin-activated inside-out vesicular Ca2+ transport and (Ca2+ + Mg2+)-ATPase alike. Our results suggest that verapamil, diltiazem and bepridil (0.01 to 0.3 mM), but not nifedipine (1 nM to 0.01 mM), in relatively high concentrations can antagonize the calmodulin-stimulated Ca2(+)-pump, i.e. the ATPase as well as the transport process. The inhibitors differed with regard to potency, selectivity, and the type of inhibition they produced.
Raess
B U
BU
Department of Pharmacology, Indiana University School of Medicine, Evansville 47732.
Record
D M
DM
D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004110:Diltiazem / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D014700:Verapamil; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D004110:Diltiazem; D002118:Calcium