Evidence for the presence of two (Ca(2+)-Mg2+) ATPases with different sensitivities to thapsigargin and cyclopiazonic acid in the human flatworm Schistosoma mansoni.
The subcellular localization of the (Ca(2+)-Mg2+)ATPase activities present in heterogeneous (P1), nuclear (P2), mitochondrial (P3) and microsomal (P4) fractions obtained by differential centrifugation of Schistosoma mansoni homogenate was investigated. In the microsomal fraction (P4), the (Ca(2+)-Mg2+)ATPase activity was completely blocked by 3 microM thapsigargin, whereas in the more heterogeneous fraction (P1), about 20-30% of this activity was resistant to the drug. The same pattern of inhibition was observed using 20 microM cyclopiazonic acid. The distribution pattern of (Ca(2+)-Mg2+)ATPase activity among the four subcellular fractions (P1 > P4 > > P3 > P2) was completely different from that of [3H]-ouabain binding sites (P1 > or = P4 = P2 > or = P3). These results indicate that the (Ca(2+)-Mg2+)ATPase in S. mansoni is predominantly of the SERCA type (localized in the endoplasmic reticulum). However, there is another enzyme, present in lower proportion that could have a plasma membrane origin (PMCA type), because it is resistant to thapsigargin and cyclopiazonic acid and its inhibition by tamoxifen is antagonized by calmodulin.
Cunha
V M
VM
Departmento De Farmacologia Básica E Clínica, Universidade Federal Do Rio De Janeiro, Cidade Universitária, Brazil.
Reis
J M
JM
Noël
F
F
D000818:Animals; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000187:drug effects* / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002147:Calmodulin / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008861:Microsomes / Q000201:enzymology; D010042:Ouabain / Q000097:blood / Q000378:metabolism; D012550:Schistosoma mansoni / Q000201:enzymology*; D013347:Subcellular Fractions; D013629:Tamoxifen / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology*
D002147:Calmodulin; D004791:Enzyme Inhibitors; D007211:Indoles; D013629:Tamoxifen; D010042:Ouabain; D019284:Thapsigargin; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; C000543:cyclopiazonic acid