VIP and PACAP regulate localized Ca²⁺ transients via cAMP-dependent mechanism

Abstract

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have been suggested as participants in enteric inhibitory neural regulation of gastrointestinal motility. These peptides cause a variety of postjunctional responses including membrane hyperpolarization and inhibition of contraction. Neuropeptides released from enteric motor neurons can elicit responses by direct stimulation of smooth muscle cells as opposed to other transmitters that rely on synapses between motor nerve terminals and interstitial cells of Cajal. Therefore, we studied the responses of murine colonic smooth muscle cells to VIP and PACAP(1-38) with confocal microscopy and patch-clamp technique. Localized Ca2+ transients (Ca2+ puffs) were observed in colonic myocytes, and these events coupled to spontaneous transient outward currents (STOCs). VIP and PACAP increased Ca2+ transients and STOC frequency and amplitude. Application of dibutyryl cAMP had similar effects. The adenylyl cyclase blocker MDL-12,330A alone did not affect spontaneous Ca2+ puffs and STOCs but prevented responses to VIP. Disruption of A-kinase-anchoring protein (AKAP) associations by application of AKAP St-Ht31 inhibitory peptide had effects similar to those of MDL-12,330A. Inhibition of ryanodine receptor channels did not block spontaneous Ca2+ puffs and STOCs but prevented the effects of dibutyryl cAMP. These findings suggest that regulation of Ca2+ transients (which couple to activation of STOCs) may contribute to the inhibitory effects of VIP and PACAP. Regulation of Ca2+ transients by VIP and PACAP occurs via adenylyl cyclase, increased synthesis of cAMP, and PKA-dependent regulation of ryanodine receptor channels.

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

“…On murine colonic smooth muscle cells, PACAP increases the frequency of Ca 2ϩ transients, as well as the frequency and amplitude of spontaneous outward currents through activation of the AC pathway (Hagen et al, 2006). In colon-inferior mesenteric ganglion neurons, PACAP causes prolonged depolarization and intense generation of fast excitatory postsynaptic potentials and action potentials through PAC1-R (Ermilov et al, 2004).…”

cAMP-activated Ca2+ signaling is required for CFTR-mediated serous cell fluid secretion in porcine and human airways

“…The strong temporal correlation between dynamic [Ca 2+ ] i and volume changes was unexpected. While VIP has been linked to Ca 2+ signaling in some cell types (10,(19)(20)(21)(22)(23)(24)(25), the mechanisms involved are unclear, and VIP has been assumed to activate airway gland fluid secretion solely by raising [cAMP] Figure 1F). Responses remained intact in control cells (Figure 1G Figure 1C and Supplemental Figure 1).…”

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

“…As a neurotransmitter, PACAP is present in the splanchnic nerve terminal and released preferentially under elevated sym-pathetic firing to elicit adrenal medullary catecholamine release (16,22,23). The predominant PACAP target receptor in the adrenal medulla is the high affinity PAC 1 -R, a G s -linked receptor that activates adenylate cyclase to increase cyclic adenosine monophosphate (cAMP) (24,25). Recent studies have shown that PACAP stimulation activates the stimulatory exchange protein activated by cAMP (Epac) pathway through the elevation in cAMP (26,27), triggering phospholipase C and a protein kinase C (PKC)-dependent subthreshold depolarization that is necessary for catecholamine release from chromaffin cells (16).…”