Role of pituitary adenylyl cyclase-activating polypeptide in intracellular calcium dynamics of neurons and satellite cells in rat superior cervical ganglia

Abstract

Pituitary adenylyl cyclase-activating polypeptide (PACAP) is a bioactive peptide with diverse effects in the nervous system. The present study investigated whether stimulation of PACAP receptors (PACAPRs) induces responses in neurons and satellite cells of the superior cervical ganglia (SCG), with special reference to intracellular Ca²⁺ ([Ca²⁺]_i) changes. The expression of PACAPRs in SCG was detected by reverse transcription-PCR. PACAP type 1 receptor (PAC1R), vasoactive intestinal peptide receptor type (VPAC)1R, and VPAC2R transcripts were expressed in SCG, with PAC1R showing the highest levels. Confocal microscopy analysis revealed that PACAP38 and PACAP27 induced an increase in [Ca²⁺]_i in SCG, first in satellite cells and subsequently in neurons. Neither extracellular Ca²⁺ removal nor Ca²⁺ channel blockade affected the PACAP38-induced increase in [Ca²⁺]_i in satellite cells; however, this was partly inhibited in neurons. U73122 or xestospongin C treatment completely and partly abrogated [Ca²⁺]_i changes in satellite cells and in neurons, respectively, whereas VPAC1R and VPAC2R agonists increased [Ca²⁺]_i in satellite cells only. This is the first report demonstrating the expression of PACAPRs specifically, VPAC1 and VPAC2 in SCG and providing evidence for PACAP38-induced [Ca²⁺]_i changes in both satellite cells and neurons via Ca²⁺ mobilization.