PAC1 Receptor Activation by PACAP-38 Mediates Ca2+ Release from a cAMP-dependent Pool in Human Fetal Adrenal Gland Chromaffin Cells

Abstract

Previous studies have shown that human fetal adrenal gland from 17-to 20-week-old fetuses expressed pituitary adenylate cyclase-activating polypeptide (PACAP) receptors, which were localized on chromaffin cells. Pituitary adenylate cyclase-activating polypeptide is a 38-residue ␣-amidated neuropeptide (PACAP-38) 1 originally isolated from the ovine hypothalamus for its ability to stimulate cAMP formation in rat anterior pituitary cells. Processing of PACAP-38 can generate a 27-amino acid amidated peptide (PACAP-27) that exhibits 68% sequence identity with vasoactive intestinal polypeptide (VIP), thus identifying PACAP as a member of the VIP/secretin/glucagon superfamily of regulatory peptides (1, 2).The effects of PACAP are mediated through interaction with two types of high affinity receptors: type I receptors are selectively activated by PACAP, whereas type II receptors bind PACAP and VIP with similar affinity (3). Three isoforms of PACAP receptors have now been cloned and designated as PACAP-specific receptor I (PAC 1 -R) (4, 5) and VIP/PACAP mutual receptors 1 and 2 (VPAC 1 -R and VPAC 2 -R) (6, 7). Both PAC 1 -R (type 1 receptors) and VPAC 1 -R/VPAC 2 -R (type 2 receptors) belong to the seven-transmembrane domain, G-protein-coupled receptor family, and are all positively coupled to adenylyl cyclase (2). Eight isoforms of PAC 1 -R, resulting from alternative splicing, have been characterized to date. These variants display differential signal transduction properties with regard to adenylyl cyclase and phospholipase C (PLC) stimulation (1, 2). In addition to these classical signaling pathways, PACAP has been found to stimulate a Ca 2ϩ -calmodulin nitric oxide synthase (8) and mitogen-activated protein kinase activity (9). These various transduction mechanisms are involved in the neurotrophic activities exerted by PACAP (i.e. inhibition of apoptosis and stimulation of neurite outgrowth) during development (9 -11).PACAP and its receptors are actively expressed in the adrenal medulla (12)(13)(14). In particular, we have previously demonstrated the occurrence of PACAP-38 (15) and PACAP binding sites (16) in chromaffin cells from 16-to 20-week-old fetal human adrenal glands. Activation of these receptors by PACAP-38 causes stimulation of cAMP production and induces a modest increase in inositol 1,4,5-triphosphate (IP 3 ) formation (16), suggesting a role for the neuropeptide in the developing

VPAC Receptor Modulation of Neuroexcitability in Intracardiac Neurons

“…Previous studies have shown that rat intracardiac neurons express three PAC 1 receptor isoforms (PAC 1 -short, PAC 1 -HOP1, and PAC 1 -HOP2) as well as VPAC 1 and VPAC 2 receptors (37). The predominant PAC 1 receptor, PAC 1 -HOP, has been shown to evoke release of calcium from intracellular stores via both cAMP and IP 3 pathways in various cell types including neuroepithelial cells, chromaffin cells, astrocytes, and cortical neurons (44,53,54). However, our data indicate that stimulation of PAC 1 has no direct effect on [Ca 2ϩ ] i in neonatal rat intracardiac neurons.…”

DREAM Mediates cAMP-Dependent, Ca2+-Induced Stimulation of GFAP Gene Expression and Regulates Cortical Astrogliogenesis

“…It is well established that PACAP increases [Ca 2ϩ ] i by mobilizing intracellular pools or by increasing extracellular calcium influx (Chatterjee et al, 1996;Przywara et al, 1996;Osipenko et al, 2000;Morita et al, 2002;Liu et al, 2003;Payet et al, 2003). Our data favor the notion that in cortical precursors PACAP promotes calcium entry from the extracellular milieu, in agreement with previous reports indicating that PACAPinduced Ca 2ϩ influx requires the activation of cAMP-dependent signaling (Przywara et al, 1996;Osipenko et al, 2000).…”

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…Incubation of adrenomedullary cells in calcium-free medium or blockage of voltage-operated calcium channels suppresses the PACAP-evoked stimulation of catecholamine secretion (Isobe et al, 1993;Houchi et al, 1995; PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE Przywara et al, 1996;O'Farrell and Marley, 1997), indicating that the effect of PACAP on chromaffin cells is mediated through calcium influx. Concurrently, in bovine and human, PACAP increases calcium levels from ryanodine/caffeine-sensitive calcium stores (Houchi et al, 1995;Tanaka et al, 1996Tanaka et al, , 1998Shibuya et al, 1999;Payet et al, 2003). The effect of PACAP on catecholamine release is associated with an increase in the expression of tyrosine hydroxylase, dopamine ␤-hydroxylase, and phenylethanolamine N-methyltransferase (Houchi et al, 1994;Rius et al, 1994;Isobe et al, 1996;Marley et al, 1996;Tönshoff et al, 1997;Hong et al, 1998;Choi et al, 1999;Park et al, 1999).…”