Alpha2B-adrenoceptors couple to Ca2+ increase in both endogenous and recombinant expression systems

Area of Science:

• Pharmacology
• Cell Biology
• Neuroscience

Background:

• Alpha2B-adrenoceptors are G protein-coupled receptors involved in various physiological processes.
• Understanding their signaling mechanisms, particularly calcium (Ca2+) mobilization, is crucial for drug development.

Purpose of the Study:

• To investigate the ability of cloned human alpha2B-adrenoceptors expressed in Sf9 cells and endogenous receptors in NG 108-15 cells to increase intracellular Ca2+.
• To characterize the relationship between receptor expression density and Ca2+ signaling.
• To determine the potency and efficacy of various agonists at alpha2B-adrenoceptors.

Main Methods:

• Heterologous expression of human alpha2B-adrenoceptors in Sf9 insect cells.
• Measurement of intracellular Ca2+ levels in response to agonist stimulation in both Sf9 and NG 108-15 cells.
• Determination of agonist potency (EC50) and efficacy.

Main Results:

• Alpha2B-adrenoceptor-expressing Sf9 cells showed significantly greater Ca2+ increases compared to NG 108-15 cells.
• In Sf9 cells, Ca2+ increase magnitude correlated positively with receptor expression density, while EC50 for noradrenaline correlated negatively.
• Agonist potency order was D-medetomidine > noradrenaline ≈ clonidine > oxymetazoline; clonidine and UK14,304 were weak partial agonists.
• Ca2+ increases in Sf9 cells involved both intracellular store mobilization and extracellular influx.
• Alpha2B-adrenoceptor stimulation in Sf9 cells increased inositol 1,4,5-trisphosphate mass.

Conclusions:

• Alpha2B-adrenoceptors can effectively couple to increase intracellular Ca2+ levels.
• This signaling may involve the activation of phospholipase C.
• Receptor expression density influences the magnitude of the Ca2+ response.