Adenosine triphosphate - dependent calcium binding and accumulation by guinea pig cardiac sarcolemma.
Sarcolemma isolated from guinea pig heart ventricles possessed ATP-dependent Ca2+ binding and accumulation (+ oxalate) activities which were not inhibited by sodium azide, oligomycin, or ruthenium red. Ca2+ binding and accumulation by sarcolemma were sensitive to pH, the optimum being about pH 6.8. The concentrations of ATP required for half-maximal binding and accumulation were 94.3 and 172 muM, respectively. Mg2+ up to 5 mM significantly enhanced both activities but was inhibitory at higher concentrations (greater than 10 mM). Sarcolemmal Ca2+ binding and accumulation were stimulated 100% by K+, half-maximal enhancement occurring at 5-10 mM K+. Ca2+ binding and accumulation were both saturable processes and the respective apparent Km values for Ca2+ were 16.4 and 14.3 muM. Ca2+ binding by sarcolemma was a rapid process and the bound Ca2+ was released upon depletion of ATP in the medium. It is suggested that the sarcolemmal Ca2+ transport system may well be of significance in regulation of the contraction-relaxation cycle of cardiac muscle.
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002458:Cell Fractionation; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000494:pharmacology; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium