Effects of monovalent cations on Ca2+ uptake by skeletal and cardiac muscle sarcoplasmic reticulum.
Ca(2+) transport by the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase (SERCA) is sensitive to monovalent cations. Possible K(+) binding sites have been identified in both the cytoplasmic P-domain and the transmembrane transport-domain of the protein. We measured Ca(2+) transport into SR vesicles and SERCA ATPase activity in the presence of different monovalent cations. We found that the effects of monovalent cations on Ca(2+) transport correlated in most cases with their direct effects on SERCA. Choline(+), however, inhibited uptake to a greater extent than could be accounted for by its direct effect on SERCA suggesting a possible effect of choline on compensatory charge movement during Ca(2+) transport. Of the monovalent cations tested, only Cs(+) significantly affected the Hill coefficient of Ca(2+) transport (n(H)). An increase in n(H) from approximately 2 in K(+) to approximately 3 in Cs(+) was seen in all of the forms of SERCA examined. The effects of Cs(+) on the maximum velocity of Ca(2+) uptake were also different for different forms of SERCA but these differences could not be attributed to differences in the putative K(+) binding sites of the different forms of the protein.
Beca
Sanja
S
Department of Physiology and Biophysics, University of Calgary, Alta., Canada.
Aschar-Sobbi
Roozbeh
R
Ponjevic
Dragana
D
Winkfein
Robert J
RJ
Kargacin
Margaret E
ME
Kargacin
Gary J
GJ
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D020013:Calcium Signaling / Q000187:drug effects*; D002414:Cations, Monovalent / Q000494:pharmacology*; D002460:Cell Line; D002586:Cesium / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D004285:Dogs; D006321:Heart / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D002414:Cations, Monovalent; D002586:Cesium; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002794:Choline