Time-Dependent Effects of the Neuropeptide PACAP on Catecholamine Secretion

Abstract

Abstract-Pituitary adenylyl cyclase-activating polypeptide (PACAP) is a potent endogenous secretagogue for chromaffin cells. We previously reported that PACAP coupled to the PAC1 receptor to evoke dihydropyridine-sensitive early (15 to 20 minutes) catecholamine secretion and cAMP response element binding protein-mediated trans-activation of the secretory protein chromogranin A promoter in PC12 pheochromocytoma cells. In this report, we studied whether the secretory and transcriptional responses elicited by PACAP were subject to desensitization. We found that PACAP evoked distinct immediate (initial, 0 to 20 minutes) and long-lasting (20 to 180 minutes) effects on catecholamine secretion. Initial secretory and chromogranin A trans-activation responses induced by PACAP were desensitized in a dose-dependent fashion after preexposure of cells to PACAP, and the IC 50 doses of PACAP for desensitization were Ϸ18-to Ϸ32-fold lower than the EC 50 activating doses for secretion or transcription. Desensitization of the initial secretion response was associated with decreased Ca 2ϩ influx through L-type voltage-operated Ca 2ϩ channels. Acute exposure to PACAP also triggered long-lasting (up to 3 hours), extracellular Ca 2ϩ -dependent, pertussis toxin-insensitive catecholamine secretion; indeed, even after short-term (20 minutes) exposure to PACAP and removal of the secretagogue, PC12 cells continued to secrete norepinephrine up to 76.9Ϯ0.22% of cellular norepinephrine content after 3 hours. A phospholipase C-␤ inhibitor (U-73122) blocked this extended secretory response, which was dependent on low-magnitude Ca 2ϩ influx resistant to several L-, N-, P/Q-, or T-type Ca 2ϩ channel antagonists, but sensitive to Zn 2ϩ , Ni 2ϩ , Cd 2ϩ , or to the store-operated Ca 2ϩ channel blocker SKF96365. A less than additive effect of the sarcoendoplasmic reticulum Ca 2ϩ -ATPase inhibitor thapsigargin plus PACAP on this sustained secretion also supported a contribution of store-operated Ca 2ϩ entry to the sustained secretory response. We propose that PACAP-evoked secretion and transcription are subject to homologous desensitization in PC12 cells; however, PACAP also induces long-lasting secretion, even under dose and time circumstances in which acute, dihydropyridine-sensitive secretion has been desensitized. Although initial secretion is mediated by an L-type voltage-operated Ca 2ϩ channel, extended secretion may involve a store-operated Ca 2ϩ channel that is activated through a G q/11 /phospholipase C-␤/phosphoinositide signaling pathway. (Hypertension. 1999;34:1152-1162.)

Heritability and Genome-Wide Linkage in US and Australian Twins Identify Novel Genomic Regions Controlling Chromogranin A

“…CHGA transcription and exocytotic secretion are controlled by the neuropeptide PACAP and its G protein-coupled receptor PAC1 on chromaffin cells. 37,38 Notably, several genes pertinent to the physiological pathway for catestatin biosynthesis and action are not in the catestatin-linked genomic regions on chromosomes 4 and 17 identified by this study. CHGA, the potential cis-QTL, is on chromosome 14q32.…”

Inhibition of Apoptosis by P2Y2Receptor Activation: Novel Pathways for Neuronal Survival

“…Dissociated cultures were grown on laminin/poly-D-lysine/collagen-coated plates for 96 h in Neurobasal A (Invitrogen) with B27 supplement (Invitrogen) and FUDR (fluoro-2Ј-deoxyuridine) (Sigma). Pheochromocytoma 12 (PC12) cells were grown as described previously (Taupenot et al, 1999).…”

Pituitary Adenylate Cyclase-activating Peptide (PACAP) Recruits Low Voltage-activated T-type Calcium Influx under Acute Sympathetic Stimulation in Mouse Adrenal Chromaffin Cells

“…Under Low Hz stimulation, the splanchnic nerve was stimulated for 60 pulses at a frequency of 0. Initial characterization has shown that PACAP-mediated stimulation depends on an influx of external Ca 2ϩ but that the cells do not fire action potentials (15,44). We set out to investigate the cellular mechanism by which PACAP evokes calcium influx in the absence of action potential firing to achieve catecholamine release from adrenal chromaffin cells.…”

“…Several factors predict that T-type Ca 2ϩ channels are a likely component of acute PACAP stimulation. Previous studies have shown that acute PACAP stimulation elicits a voltage-dependent influx of external calcium that is independent of the major high voltage-activated Ca 2ϩ channels (15,44). Moreover, PACAP stimulation leads to an up-regulation of protein kinase C activity (16,45,46).…”