Ca2+ Imaging in Perfused Adrenal Medullae

American Journal of Physiology-Cell Physiology

et al. 2012

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Muscarinic receptors are expressed in the adrenal medullary (AM) cells of various mammals, but their physiological roles are controversial. Therefore, the ionic mechanism for muscarinic receptor-mediated depolarization and the role of muscarinic receptors in neuronal transmission were investigated in dissociated guinea-pig AM cells and in the perfused guinea-pig adrenal gland. Bath application of muscarine induced an inward current at Ϫ60 mV. This inward current was partially suppressed by quinine with an IC50 of 6.1 M. The quinineinsensitive component of muscarine-induced currents changed the polarity at Ϫ78 mV and was inhibited by bupivacaine, a TWIKrelated acid-sensitive K ϩ (TASK) channel inhibitor. Conversely, the current-voltage relationship for the bupivacaine-insensitive component of muscarine currents showed a reversal potential of Ϫ5 mV and a negative slope below Ϫ40 mV. External application of La 3ϩ had a double action on muscarine currents of both enhancement and suppression. Immunoblotting and immunocytochemistry revealed expression of TASK1 channels and cononical transient receptor potential channels 1, 4, 5, and 7 in guinea-pig AM cells. Retrograde application of atropine reversibly suppressed transsynaptically evoked catecholamine secretion from the adrenal gland. The results indicate that muscarinic receptor stimulation in guinea-pig AM cells induces depolarization through inhibition of TASK channels and activation of nonselective cation channels and that muscarinic receptors are involved in neuronal transmission from the splanchnic nerve.

Section: Methodsmentioning

confidence: 99%

“…The adrenal gland was placed between one pair of silver circles for electrical stimulation, and then the gland was transferred to a chamber. Catecholamines secreted from AM cells were measured using the amperometric method (54).…”

Section: Methodsmentioning

confidence: 99%

Mechanisms and roles of muscarinic activation in guinea-pig adrenal medullary cells

Inoue

American Journal of Physiology-Cell Physiology

et al. 2012

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“…Embryonic rat chromaffin cells, just before birth, exhibited an increase in intracellular Ca 2+ concentration in response to stimulation of nAChRs, but not of muscarinic receptors, whereas cells after birth responded to muscarinic receptor stimulation as well. Muscarinic receptors are responsible for part of neuronal transmission in guinea pig chromaffin cells (Inoue et al ., ; Warashina and Inoue, ). Taken together with phylogenic and ontogenic considerations, this result suggests that muscarinic signalling in chromaffin cells develops to help animals cope with life‐threatening stress.…”

Section: Discussionmentioning

confidence: 97%

Identification of muscarinic receptor subtypes involved in catecholamine secretion in adrenal medullary chromaffin cells by genetic deletion

Miyata

et al. 2015

British J Pharmacology

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BACKGROUND AND PURPOSEActivation of muscarinic receptors results in catecholamine secretion in adrenal chromaffin cells in many mammals, and muscarinic receptors partly mediate synaptic transmission from the splanchnic nerve, at least in guinea pigs. To elucidate the physiological functions of muscarinic receptors in chromaffin cells, it is necessary to identify the muscarinic receptor subtypes involved in excitation. EXPERIMENTAL APPROACHTo identify muscarinic receptors, pharmacological tools and strains of mice where one or several muscarinic receptor subtypes were genetically deleted were used. Cellular responses to muscarinic stimulation in isolated chromaffin cells were studied with the patch clamp technique and amperometry. KEY RESULTSMuscarinic M1, M4 and M5 receptors were immunologically detected in mouse chromaffin cells, and these receptors disappeared after the appropriate gene deletion. Mouse cells secreted catecholamines in response to muscarinic agonists, angiotensin II and a decrease in external pH. Genetic deletion of M1, but not M3, M4 or M5, receptors in mice abolished secretion in response to muscarine, but not to other stimuli. The muscarine-induced secretion was suppressed by MT7, a snake peptide toxin specific for M1 receptors. Similarly, muscarine failed to induce an inward current in the presence of MT7 in mouse and rat chromaffin cells. The binding affinity of VU0255035 for the inhibition of muscarine-induced currents agreed with that for the M1 receptor. CONCLUSIONS AND IMPLICATIONSBased upon the effects of genetic deletion of muscarinic receptors and MT7, it is concluded that the M1 receptor alone is responsible for muscarine-induced catecholamine secretion. AbbreviationsHA, haemagglutinin; IR, immunoreactivity; KO, knockout; nAChR, nicotinic ACh receptor BJP British Journal of Pharmacology

“…The responses of acutely dissociated chromaffin cells to GABA conspicuously differ between rats and guinea pigs. Application of 30 μM GABA evoked inward currents in 33% of rat chromaffin cells examined (Warashina and Inoue, 2012 ), but in 100% of guinea-pig chromaffin cells (Warashina and Inoue, 2012 ). In addition, even in responding cells the amplitudes of GABA-induced currents in rat cells were tiny compared with those in guinea-pigs.…”

Section: Effects Of Gabamentioning

confidence: 99%

GABA Signaling and Neuroactive Steroids in Adrenal Medullary Chromaffin Cells

Fujihara

et al. 2016

Front. Cell. Neurosci.

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Gamma-aminobutyric acid (GABA) is produced not only in the brain, but also in endocrine cells by the two isoforms of glutamic acid decarboxylase (GAD), GAD65 and GAD67. In rat adrenal medullary chromaffin cells only GAD67 is expressed, and GABA is stored in large dense core vesicles (LDCVs), but not synaptic-like microvesicles (SLMVs). The α3β2/3γ2 complex represents the majority of GABAA receptors expressed in rat and guinea pig chromaffin cells, whereas PC12 cells, an immortalized rat chromaffin cell line, express the α1 subunit as well as the α3. The expression of α3, but not α1, in PC12 cells is enhanced by glucocorticoid activity, which may be mediated by both the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). GABA has two actions mediated by GABAA receptors in chromaffin cells: it induces catecholamine secretion by itself and produces an inhibition of synaptically evoked secretion by a shunt effect. Allopregnanolone, a neuroactive steroid which is secreted from the adrenal cortex, produces a marked facilitation of GABAA receptor channel activity. Since there are no GABAergic nerve fibers in the adrenal medulla, GABA may function as a para/autocrine factor in the chromaffin cells. This function of GABA may be facilitated by expression of the immature isoforms of GAD and GABAA receptors and the lack of expression of plasma membrane GABA transporters (GATs). In this review, we will consider how the para/autocrine function of GABA is achieved, focusing on the structural and molecular mechanisms for GABA signaling.