Effects of long-term acidification of extracellular pH on ATP-induced calcium mobilization in rabbit lens epithelial cells.
ATP-induced calcium (Ca2+) mobilization was investigated in rabbit lens epithelial cells that had been cultured in a medium with pH of 7.4 (group 1), 7.2 (group 2), or 7.0 (group 3) for 10 to 21 d. Intracellular free Ca2+ ([Ca2+]i and pH (pHi) were measured by using fluorescent dyes, fura-2 and BCECF, respectively. The long-term acidification decreased the pHi to 7.15 +/- 0.01, from 7.22 +/- 0.01, in group 2 and to 7.09 +/- 0.01 in group 3. The administration of 10 micromol/l ATP produced an initial peak followed by a sustained increase in [Ca2+]i in the lens cells of group 1. Both the initial peak and the sustained increase in [Ca2+]i were enhanced in groups 2 and 3. The initial peak was abolished by pretreatment with 1 micromol/l thapsigargin, an ER Ca2+ pump inhibitor, but was not affected by the removal of extracellular Ca2+. On the other hand, the sustained increase was suppressed either by the thapsigargin treatment or by the Ca2+ removal. Treatment with only thapsigargin caused a sustained increase in [Ca2+]i that was greater in group 3 than in group 1. These results suggest that (1) the ATP-induced initial peak in [Ca2+]i is due to Ca2+ release from the intracellular stores, (2) the sustained increase in [Ca2+]i is mediated through either Ca2+ influx from the extracellular space or Ca2+ release from the store triggered by the Ca2+ influx, and (3) long-term, moderate acidification enhances both the initial peak and the sustained increase in [Ca2+)]i in rabbit lens epithelial cells. One possible mechanism of the ATP-induced Ca2+ influx seems to be a capacitative Ca2+ entry pathway.
Yawata
K
K
Second Department of Physiology, Faculty of Medicine, Tottori University, Yonago, 683-8503 Japan.
Nagata
M
M
Narita
A
A
Kawai
Y
Y
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D018929:Cell Culture Techniques; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007908:Lens, Crystalline / Q000502:physiology*; D011817:Rabbits; D019284:Thapsigargin / Q000494:pharmacology
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D002118:Calcium