Characterization of Ca²⁺ signaling pathways in mouse adrenal medullary chromaffin cells

Abstract

J. Neurochem. (2010) 112, 1210–1222. Abstract In the present study, we characterized the Ca2+ responses and secretions induced by various secretagogues in mouse chromaffin cells. Activation of the acetylcholine receptor (AChR) by carbachol induced a transient intracellular Ca2+ concentration ([Ca2+]i) increase followed by two phases of [Ca2+]i decay and a burst of exocytic events. The contribution of the subtypes of AChRs to carbachol‐induced responses was examined. Based on the results obtained by stimulating the cells with the nicotinic receptor (nAChR) agonist, 1,1‐dimethyl‐4‐phenylpiperazinium iodide, high K+ and the effects of thapsigargin, it appears that activation of nAChRs induces an extracellular Ca2+ influx, which in turn activate Ca2+‐induced Ca2+ release via the ryanodine receptors. Muscarine, a muscarinic receptor (mAChRs) agonist, was found to induce [Ca2+]i oscillation and sustained catecholamine release, possibly by activation of both the receptor‐ and store‐operated Ca2+ entry pathways. The RT‐PCR results showed that mouse chromaffin cells are equipped with messages for multiple subtypes of AChRs, ryanodine receptors and all known components of the receptor‐ and store‐operated Ca2+ entry. Furthermore, results obtained by directly monitoring endoplasmic reticulum (ER) and mitochondrial Ca2+ concentration and by disabling mitochondrial Ca2+ uptake suggest that the ER acts as a Ca2+ source, while the mitochondria acts as a Ca2+ sink. Our results show that both nAChRs and mAChRs contribute to the initial carbachol‐induced [Ca2+]i increase which is further enhanced by the Ca2+ released from the ER mediated by Ca2+‐induced Ca2+ release and mAChR activation. This information on the Ca2+ signaling pathways should lay a good foundation for future studies using mouse chromaffin cells as a model system.

Altered adrenal chromaffin cell function during experimental colitis

“…It is important to note however that the effects of gastrointestinal inflammation on Ca 2ϩ signaling are not necessarily always inhibitory. For example, during TNBScolitis in guinea pigs, facilitation of synaptic transmission was observed within the submucosal and myenteric plexuses, which is unlikely to have resulted from decreased I Ca (37,41 (63). Although the present study did not assess the contribution of CICR to Ca 2ϩ signaling in ACCs during colitis, our results suggest that inhibition of I Ca is likely to be the primary cause of decreased Ca 2ϩ elevations.…”

“…We have previously described a decrease in I Ca of sympathetic neurons during colitis that was due to the selective inhibition of N-type Ca 2ϩ channels accompanied by a reduction in mRNA encoding the channel ␣-subunit, Ca V 2.2 (50). Therefore, we examined whether the inhibition of I Ca in ACC was associated with a selective reduction in mRNA encoding VGCC ␣-subunits in these cells: Ca V 1.2, -1.3, -2.1, -2.2, and -2.3 (3,15,29,63). Colitis caused a slight but statistically insignificant decrease in mRNA encoding Ca V 2.2, which underlies N-type channels, as well as Ca V 2.1, which underlies P/Q-type channels (Fig.…”

Endotoxemia Enhances Catecholamine Secretion From Male Mouse Adrenal Chromaffin Cells Through an Increase In Ca2+ Release From the Endoplasmic Reticulum

“…The role of CICR in mouse ACCs has also been addressed in recent studies. Caffeine stimulates Ca 2ϩ transients and decreases ER Ca 2ϩ concentration in mouse ACCs (26). Furthermore, these cells exhibit Ca 2ϩ scintillas, which are spontaneous ER Ca 2ϩ release events mediated by ryanodine receptors (70,71).…”

“…Elevations in intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) can be achieved by Ca 2ϩ influx through voltage-gated Ca 2ϩ channels and Ca 2ϩ release from the endoplasmic reticulum (ER) (23)(24)(25). The spatiotemporal properties of the resultant Ca 2ϩ signal can also be modified by intracellular organelles (26). Ca 2ϩ signaling is a plastic process that can become altered during inflammation and infection (27)(28)(29).…”

Cytosolic organelles shape calcium signals and exo–endocytotic responses of chromaffin cells

“…A later report showed that mouse chromaffin cells in the intact gland exhibited a smaller or nonexistent CICR [110]. However, in a recent study performed on cultured mouse chromaffin cells the expression of RyRs and a functional CICR mechanism was shown [111].…”