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Intracellular calcium and alpha 1b-adrenoceptor phosphorylation
J A García-Sáinz1, A Mendoza-Mendoza, J Vázquez-Prado
1Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, D.F., Mexico. agarcia@ifisiol.unam.mx
Archives of Medical Research
|December 22, 1999
Summary
Increased intracellular calcium does not directly cause alpha 1b-adrenoceptor phosphorylation. Buffering calcium levels did not affect receptor phosphorylation by most agents, suggesting calcium is not the primary driver.
Area of Science:
- Pharmacology
- Cell Signaling
- Molecular Biology
Background:
- G protein-coupled receptor (GPCR) desensitization involves receptor phosphorylation.
- Second messenger-activated protein kinases and GPCR kinases are implicated in GPCR phosphorylation.
- The specific role of intracellular calcium ([Ca2+]i) in alpha 1b-adrenoceptor phosphorylation remains unclear.
Purpose of the Study:
- To investigate the role of intracellular calcium ([Ca2+]i) in the phosphorylation of the alpha 1b-adrenoceptor.
- To determine if elevated [Ca2+]i is sufficient to induce alpha 1b-adrenoceptor phosphorylation.
Main Methods:
- Utilized Rat-1 fibroblasts expressing the hamster alpha 1b-adrenergic receptor.
- Cells were metabolically labeled with [32P]Pi to study receptor phosphorylation.
- Intracellular calcium levels were measured using Fura-2 fluorescence.
Main Results:
- Norepinephrine, endothelin-1, and lysophosphatidic acid increased [Ca2+]i and induced alpha 1b-adrenoceptor phosphorylation.
- The calcium chelator BAPTA blocked [Ca2+]i increases but did not inhibit phosphorylation by norepinephrine, PMA, or lysophosphatidic acid.
- Thapsigargin increased [Ca2+]i but failed to induce phosphorylation and reduced PMA-induced phosphorylation.
Conclusions:
- An increase in intracellular calcium ([Ca2+]i) is insufficient to induce alpha 1b-adrenoceptor phosphorylation.
- Buffering intracellular calcium does not affect alpha 1b-adrenoceptor phosphorylation induced by norepinephrine, lysophosphatidic acid, and PMA.
- A minor role for calcium in endothelin-1-induced alpha 1b-adrenoceptor phosphorylation is possible.