Vanadate-sensitive microsomal ATPases and microsomal 45Ca2+ uptake in tracheal epithelial cells.
Cytosolic free Ca2+ plays important roles in the regulation of physiological processes in tracheal epithelial cells and is probably regulated by many ion-transporting ATPases in these cells. Therefore, the effect of vanadate was investigated to characterize microsomal ion-transporting ATPases. Dose response experiments showed that vanadate had a biphasic effect on the microsomal ATPase activity: a decrease at the vanadate concentration below 100 microM, and a steep decrease at the concentration above 100 microM. The dose response data were fitted to two sigmoidal functions, corresponding to a low-affinity vanadate-sensitive (LAVS) ATPase and a high-affinity vanadate-sensitive (HAVS) ATPase. In 45Ca2+ uptake experiments, both LAVS and HAVS ATPases mediated microsomal 45Ca2+ uptake. The LAVS ATPase was selectively sensitive to thapsigargin in both ATPase activity and 45Ca2+ uptake, suggesting that it is an ER/SR-type intracellular Ca2+-ATPase. Although the HAVS ATPase mediated one-fourth of microsomal 45Ca2+ uptake, its activity was not sensitive to thapsigargin. These results indicate that the activities of these two vanadate-sensitive ATPases are mediated by different enzymes, since thapsigargin only blocks the activity of LAVS ATPase. In conclusion, there are two types of vanadate-sensitive microsomal ATPases, and these ATPases mediate microsomal 45Ca2+ uptake in airway epithelial cells.
Kim
Y K
YK
Department of Agricultural Chemistry, Chungbuk National University, Cheongju, Chungbuk, Korea. ykkim10@cbucc.chungbuk.ac.kr. ykkim10@cbucc.chungbuk.ac.kr
Sakong
J
J
Cho
K H
KH
Lee
C O
CO
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006096:Gramicidin / Q000494:pharmacology; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D013552:Swine; D019284:Thapsigargin / Q000494:pharmacology; D014132:Trachea / Q000166:cytology / Q000378:metabolism*; D014638:Vanadates / Q000378:metabolism* / Q000494:pharmacology
D002135:Calcium-Binding Proteins; D002412:Cations; D004791:Enzyme Inhibitors; D007476:Ionophores; D006096:Gramicidin; D014638:Vanadates; D019284:Thapsigargin; D000251:Adenosine Triphosphatases; D002118:Calcium