Subcellular mechanism of desensitization of the ATP-induced Ca2+ mobilization in human umbilical vein endothelial cells: role of intracellular Ca2+ stores.
Confluent monolayers of human umbilical vein endothelial cells subcultured on glass coverslips were loaded with the fluorescent Ca2+ indicator, fura-2. Changes in fura-2 fluorescence were detected by means of a fluorescence spectrophotometer. Both ATP and ADP (0.3-100 microM) caused a concentration-dependent transient peak response of the intracellular free calcium concentration ([Ca2+]i), followed by a lower sustained response. AMP and adenosine did not induce detectable changes in [Ca2+]i. The sustained response to ATP was abolished by superfusion with the Ca2(+)-free solution (with 1 mM EGTA), while the transient peak response was uninfluenced. The transient peak response to ATP (30 microM) was inhibited by pre-exposure to ATP in a graded manner depending on the concentration of ATP. The response to ATP recovered after washout for 20 min with the solution containing Ca2+, but not with the Ca2(+)-free solution. The transient peak response to ATP was markedly reduced by preceding exposure to histamine, while the response to histamine was not influenced by pre-exposure to ATP. These findings indicate that depletion and refilling of the ATP-sensitive intracellular Ca2+ store may be responsible for the desensitization and recovery of the ATP-induced [Ca2+]i response. The pharmacological characteristics of the ATP-sensitive intracellular Ca2+ store seem different from those of the histamine-sensitive store.
Ishihata
A
A
Department of Pharmacology, Yamagata University School of Medicine, Japan.
Endoh
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D011247:Pregnancy; D014471:Umbilical Veins
D004533:Egtazic Acid; D006632:Histamine; D000255:Adenosine Triphosphate; D002118:Calcium