Abstract
We constructed Chinese hamster ovary (CHO) cells stably expressing α1A-, α1B-, or α1D-adrenergic receptors (CHO-α1A, CHO-α1B, or CHO-α1D, respectively) and compared the Ca2+channels activated by noradrenaline (NA) in these cells using whole-cell recordings and monitoring of the intracellular free Ca2+ concentration ([Ca2+]i). We also investigated the involvement of Ca2+ channels in the NA-induced arachidonic acid release. In all three cell types, NA at concentrations ≥10 nM induced a sustained increase in [Ca2+]i attributable to extracellular Ca2+ influx in [Ca2+]i monitoring and an inward current in whole-cell recording. The current-voltage relationships were linear, and their reversal potentials were close to 0 mV. The reversal potential of the currents was not affected by a change in the concentration of Cl− in the bath solution. Moreover, a current could be induced in a bath solution containing only Ca2+ as the movable cation. LOE 908, a receptor-operated Ca2+ channel blocker, inhibited the sustained increase in [Ca2+]i and inward currents in a concentration-dependent manner, and complete inhibition was observed at concentrations ≥ 3 μM. NA induced arachidonic acid release in all three cell types. This release was entirely dependent on extracellular Ca2+ influx. Moreover, LOE 908 at concentrations ≥ 3 μM blocked the NA-induced increase in arachidonic acid release. These results indicate that 1) NA activates LOE 908-sensitive Ca2+-permeable nonselective cation channels (NSCCs) in CHO-α1A, CHO-α1B, and CHO-α1D, and 2) the Ca2+ influx through NSCCs may play an important role in the NA-induced enhancement of arachidonic acid release in these cells.
Footnotes
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Send reprint requests to: Dr. Yoshifumi Kawanabe, Department of Neurosurgery, Kyoto University Faculty of Medicine, 54 Shougoin-Kawaharachou, Sakyo-ku, Kyoto 606-8501, Japan. E-mail:kawanabe{at}kuhp.kyoto-u.ac.jp
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Supported by a grant-in-aid from the Ministry of Education, Science, Sports and Culture of Japan, by Special Coordination Funds for Science and Technology from the Science and Technology Agency (STA), by a Research Grant for Cardiovascular Disease (11C-1) from the Ministry of Health and Welfare, and by a grant from the Smoking Research Foundation, Japan.
- Abbreviations:
- AR
- adrenergic receptor
- [Ca2+]i
- intracellular free Ca2+concentration
- CHO
- Chinese hamster ovary
- IPs
- inositol phosphates
- NA
- noradrenaline
- NMDG
- N-methyl-d-glucamine
- NSCC
- nonselective cation channel
- SOCC
- store-operated Ca2+ channel
- VOCC
- voltage-operated Ca2+ channel
- FCS
- fetal calf serum
- Received July 3, 2001.
- Accepted August 13, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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