SAT-078 Adrenergic Receptor Regulation of Intracellular Calcium in Human Adrenocortical Carcinoma HAC15 Cells

Abstract

Intracellular calcium fluctuations may play a role in the control of corticosteroid synthesis and secretion by the adrenal cortex. Using live-cell imaging with the calcium-sensitive fluorescent probe Fluo-4 in a human adrenocortical carcinoma cell line (HAC15), we previously demonstrated that activation of M3 muscarinic receptors stimulates intracellular calcium oscillations, enhances aldosterone production, and increases expression of CYP11B2 (1). To further understand autonomic control of cortical cell function, we are investigating the role of adrenergic signalers in regulating calcium homeostasis in HAC15 cells. Activation of adrenergic receptors with the endogenous, non-selective agonists norepinephrine and epinephrine (10μM) causes single, large calcium transients that do not oscillate. A similar calcium response results from the alpha adrenergic agonist phenylephrine, while the beta adrenergic agonist terbutaline does not elicit calcium changes. Consistent with this, norepinephrine-induced calcium changes are blocked by the alpha adrenergic antagonist phentolamine, but not by the beta adrenergic antagonist propranolol. Taken together, these preliminary results suggest that alpha adrenergic receptors are the dominant adrenergic subtype in the human adrenal cortex. Further experiments will use radiolabel binding assays, subtype-selective alpha receptor modulators, and RT-PCR methods, to determine which alpha subtypes are present. Also, ELISA measurements of steroid production will determine the physiological consequence of adrenergic receptor activation.