Protein Kinase C Agonists Increase the Expression of Angiotensin II Receptors in Neuronal Cultures

Previous studies have shown that norepinephrine is important in the regulation of central angiotensin II receptors, an effect mediated by alpha 1-adrenergic receptors. Because alpha 1-adrenergic stimulation leads to inositol phospholipid hydrolysis and activation of protein kinase C, we have examined a possible role of this enzyme in the regulation of central angiotensin II (Ang II) receptors. In the present study, we have examined the effects of protein kinase C activators, phorbol esters, on the expression of Ang II receptors in neuronal cultures prepared from 1-day-old rat brains. The active phorbol ester phorbol-12-myristate-13-acetate (TPA) caused time- and concentration-dependent increases in the specific binding of [125I]Ang II to its receptors in neuronal cultures of normotensive and spontaneously hypertensive rat brains. The stimulatory effect of TPA on Ang II receptors was apparent within 15 min and reached a maximum between 1 and 2 h. Ang II specific binding had returned to control levels by 24 h. Various phorbol esters increased [125I]Ang II binding in accordance with their order of potency in stimulating protein kinase C activity. Saturation and Scatchard analysis revealed that the phorbol ester-induced increase in [125I]Ang II binding was due to an increase in the number of Ang II receptors. These observations indicate that activation of protein kinase C results in an increased expression of Ang II receptors in neuronal cultures from both normotensive and spontaneously hypertensive rat brains. The results suggest a possible role of phosphorylation in Ang II receptor expression in neuronal cultures.