Possible Involvement of Ryanodine Receptor-Mediated Intracellular Calcium Release in the Effect of Corticotropin-Releasing Factor on Adrenocorticotropin Secretion

Abstract

We examined the role of intracellular calcium release in the regulation of CRH-induced ACTH secretion using the AtT20 corticotroph cell line. We found that ruthenium red, an inhibitor of ryanodine receptor, substantially diminished the secretory response, whereas Xestospongin C, an inositol 1,4,5-triphosphate receptor antagonist, had no effect. Expression of two ryanodine receptor subtypes (RyR1 and RyR3) was confirmed by RT-PCR. We also found that caffeine, a ryanodine receptor agonist, significantly stimulated, whereas thapsigargin, which causes depletion of intracellular calcium store, markedly diminished, the ACTH release. These results suggest that ryanodine receptor-mediated calcium-induced calcium release is involved in the regulation of CRH-induced ACTH release.

Roles of Protein Kinase A (PKA) and PKC on Corticotropin-Releasing Hormone (CRH)-Induced Elevation of Cytosolic Calcium from Extra- and Intra-cellular Sources

“…To this point, our data are in agreement with published reports showing that CRH induces calcium ion entrance from extra-cellular 2,5,[15][16][17][18] and/or intra-cellular sources 3,6,7,15,16,19,20 .…”

“…The inhibitor of PKC phosphorylation, the pseudo-substrate myristoylated alanine-rich PKC [20][21][22][23][24][25][26][27][28] (Myr-N-FARK-GALRQ-NH 2 ) and the inhibitor of PKA phosphorylation, myristoylated PKA [14][15][16][17][18][19][20][21][22] (Myr-GRTGR-RNAI-NH2) were obtained from Calbiochem (La Jolla, CA) while the activator of conventional and novel PKC isoenzymes, phorbol 12-myristate 13-ace-…”

“…Figure 1, panel A depicts the effect of CRH at 1 nM which induced an acute elevation of cytosolic calcium ions. Figure 1, panel D depicts the effect of the simultaneous presence of the PKA phosphorylation inhibitor myristoylated PKA [14][15][16][17][18][19][20][21][22] at 100 ìÌ on CRH-induced calcium ion elevation in PC12 cells in a calcium rich environment. Indeed, the PKA inhibitor prevented the stimulatory effect of CRH suggesting that PKA-dependent signalling pathways mediate its effect.…”

“…Indeed, the PKA inhibitor prevented the stimulatory effect of CRH suggesting that PKA-dependent signalling pathways mediate its effect. Compared to CRH alone, the simultaneous presence of the activator of PKC phorbol 12-myristate 13-acetate (PMA) at 200 nM ( Figure 1, panel B) or of the PKC phosphorylation inhibitor pseudo-substrate myristoylated alanine-rich PKC [20][21][22][23][24][25][26][27][28] at 100 ìM ( Figure 1, panel E) did not significantly alter the steep of the curve depicting the rate of cytosolic calcium ion elevation suggesting that the PKC signalling pathway was not part of the CRH-induced calcium ion influx.…”

Gene array profiling of large hypothalamic CNS regions in lactating and randomly cycling virgin mice

“…The novel finding of decreases in L mice of the endothelin receptor b, a receptor involved in vasoconstriction [46], could provide a mechanism for the elevated levels of hemoglobin RNA we find (Table 2). We find elevated synthesis of ryanodine receptor 3 message and functionally this receptor has been linked to elevated peptide release [52] that could reflect increased peptidergic signaling in L mice. Interestingly, the finding of downregulation of syntaptotagmin, a key molecule in the calcium-induced release of small vesicles [18], implies a possible concomitant decrease in fast neurotransmitter release during lactation.…”