Related Experiment Videos
Mepacrine blocks beta-adrenergic agonist-induced desensitization in astrocytoma cells
Abstract:
C6 astrocytoma cells contain beta-adrenergic receptors coupled to adenylate cyclase. A 2-hr exposure to l-isoproterenol results in an 80% decrease in cyclic AMP production in response to a subsequent challenge by l-isoproterenol (desensitization). This loss in responsiveness is paralleled by a 20-30% decrease in the apparent number of beta-adrenergic receptors and by increased release of arachidonic aciid into the medium. The increased release of arachidonic acid is caused by the action of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) and corresponds to increased turnover of methylated phospholipids. Mepacrine and tetracaine, both inhibitors of this phospholipase A2, are able to block l-isoproterenol-induced desensitization of cyclic AMP production and the decrease in beta-adrenergic receptors. Mellitin and phorbol ester, two activators of phospholipase A2, when preincubated with the cells cause a decreased cyclic AMP response of the cells to l-isoproterenol. These results suggest that the activation of phospholipase A2 in the local domain of the beta-adrenergic receptor may be involved in desensitization.
Insights
Beta-adrenergic receptor desensitization in C6 astrocytoma cells involves phospholipase A2 activation. This enzyme
Area of Science:
- Cellular signaling
- Neuropharmacology
- Biochemistry
Background:
- C6 astrocytoma cells possess beta-adrenergic receptors linked to adenylate cyclase.
- Exposure to l-isoproterenol induces desensitization, reducing cyclic AMP production.
- This desensitization is accompanied by decreased receptor numbers and increased arachidonic acid release.
Purpose of the Study:
- To investigate the role of phospholipase A2 in beta-adrenergic receptor desensitization.
- To explore the mechanism linking receptor activation to reduced cellular responsiveness.
Main Methods:
- Utilized C6 astrocytoma cells for experiments.
- Measured cyclic AMP production following l-isoproterenol challenge.
- Assessed beta-adrenergic receptor numbers.
- Quantified arachidonic acid release.
- Employed phospholipase A2 inhibitors (mepacrine, tetracaine) and activators (mellitin, phorbol ester).
Main Results:
- l-isoproterenol exposure led to desensitization, decreased beta-adrenergic receptors, and increased arachidonic acid release.
- Increased arachidonic acid release correlated with methylated phospholipid turnover, indicating phospholipase A2 activity.
- Inhibitors of phospholipase A2 blocked desensitization and receptor number decrease.
- Activators of phospholipase A2 mimicked desensitization effects.
Conclusions:
- Phospholipase A2 activation appears to play a critical role in beta-adrenergic receptor desensitization.
- The findings suggest that phospholipase A2 activity in the receptor's vicinity contributes to the loss of cellular responsiveness.