Activation of a calcium entry pathway by sodium pyrithione in the bag cell neurons of Aplysia

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Intracellular Ca2+ is influenced by both Ca2+ influx and release. We examined intracellular Ca2+ following action potential firing in the bag cell neurons of Aplysia californica. Following brief synaptic input, these neuroendocrine cells undergo an afterdischarge, resulting in elevated Ca2+ and the secretion of neuropeptides to initiate reproduction. Cultured bag cell neurons were injected with the Ca2+ indicator, fura-PE3, and subjected to simultaneous imaging and electrophysiology. Delivery of a 5-Hz, 1-min train of action potentials (mimicking the fast phase of the afterdischarge) produced a Ca2+ rise that markedly outlasted the initial influx, consistent with Ca2+-induced Ca2+ release (CICR). This response was attenuated by about half with ryanodine or depletion of the endoplasmic reticulum (ER) by cyclopiazonic acid. However, depletion of the mitochondria, with carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone, essentially eliminated CICR. Dual depletion of the ER and mitochondria did not reduce CICR further than depletion of the mitochondria alone. Moreover, tetraphenylphosphonium, a blocker of mitochondrial Ca2+ release, largely prevented CICR. The Ca2+ elevation during and subsequent to a stimulus mimicking the full afterdischarge was prominent and enhanced by protein kinase C activation. Traditionally, the ER is seen as the primary Ca2+ source for CICR. However, bag cell neuron CICR represents a departure from this view in that it relies on store interaction, where Ca2+ released from the mitochondria may in turn liberate Ca2+ from the ER. This unique form of CICR may be used by both bag cell neurons, and other neurons, to initiate secretion, activate channels, or induce gene expression.

Section: Reagents and Drug Applicationsupporting

confidence: 86%

Ca²⁺-Induced Ca²⁺Release inAplysiaBag Cell Neurons Requires Interaction Between Mitochondrial and Endoplasmic Reticulum Stores

Geiger

Magoski²

2008

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“…Such changes can modulate the function of several ion channels (Chen and Chesler 2015), including voltage-gated Ca 2ϩ channels (Zhou and Jones 1996), or influence the pH-dependent processes required for mitochondrial Ca 2ϩ uptake and H ϩ /Ca 2ϩ exchanger-mediated Ca 2ϩ release (Jiang et al 2009; Santo-Domingo and Demaurex 2010). That stated, it is doubtful that the activation of the PMCA during voltage-gated Ca 2ϩ influx has a substantial effect on intracellular pH in the present study, as prior work has shown that Ca 2ϩ derived from other channels does not alter the acidity of the cytosol (Knox et al 2004). Even if such changes occurred, it is unlikely that disrupting proton transport by the PMCA would enhance bag cell neuron CICR by modulating voltage-gated Ca 2ϩ channels or mitochondrial Ca 2ϩ release.…”

Section: Discussionmentioning

confidence: 66%

Ca²⁺removal by the plasma membrane Ca²⁺-ATPase influences the contribution of mitochondria to activity-dependent Ca²⁺dynamics inAplysianeuroendocrine cells

Groten

Rebane

Hodgson

et al. 2016

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After Ca(2+) influx, mitochondria can sequester Ca(2+) and subsequently release it back into the cytosol. This form of Ca(2+)-induced Ca(2+) release (CICR) prolongs Ca(2+) signaling and can potentially mediate activity-dependent plasticity. As Ca(2+) is required for its subsequent release, Ca(2+) removal systems, like the plasma membrane Ca(2+)-ATPase (PMCA), could impact CICR. Here we examine such a role for the PMCA in the bag cell neurons of Aplysia californica CICR is triggered in these neurons during an afterdischarge and is implicated in sustaining membrane excitability and peptide secretion. Somatic Ca(2+) was measured from fura-PE3-loaded cultured bag cell neurons recorded under whole cell voltage clamp. Voltage-gated Ca(2+) influx was elicited with a 5-Hz, 1-min train, which mimics the fast phase of the afterdischarge. PMCA inhibition with carboxyeosin or extracellular alkalization augmented the effectiveness of Ca(2+) influx in eliciting mitochondrial CICR. A Ca(2+) compartment model recapitulated these findings and indicated that disrupting PMCA-dependent Ca(2+) removal increases CICR by enhancing mitochondrial Ca(2+) loading. Indeed, carboxyeosin augmented train-evoked mitochondrial Ca(2+) uptake. Consistent with their role on Ca(2+) dynamics, cell labeling revealed that the PMCA and mitochondria overlap with Ca(2+) entry sites. Finally, PMCA-dependent Ca(2+) extrusion did not impact endoplasmic reticulum-dependent Ca(2+) removal or release, despite the organelle residing near Ca(2+) entry sites. Our results demonstrate that Ca(2+) removal by the PMCA influences the propensity for stimulus-evoked CICR by adjusting the amount of Ca(2+) available for mitochondrial Ca(2+) uptake. This study highlights a mechanism by which the PMCA could impact activity-dependent plasticity in the bag cell neurons.

“…Nevertheless, reports continue to assert that certain neurons either lack or show limited store-operated Ca 2+ influx (Chinopoulos et al 2004;Emptage et al 2001;Grimaldi et al 2001;Koizumi et al 1999). The ongoing controversy prompted us to explore this pathway in the bag cell neurons of the marine mollusk, Aplysia californica-a preparation in which the regulation of intracellular Ca 2+ has been extensively investigated (Fink et al 1988;Jonas et al 1997;Knox et al 1996Knox et al , 2004Magoski et al 2000).…”

Section: Introductionmentioning

confidence: 99%

A Store-Operated Ca²⁺Influx Pathway in the Bag Cell Neurons ofAplysia

Kachoei

Knox²,

Uthuza³

et al. 2006

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Although store-operated Ca(2+) influx has been well-studied in nonneuronal cells, an understanding of its nature in neurons remains poor. In the bag cell neurons of Aplysia californica, prior work has suggested that a Ca(2+) entry pathway can be activated by Ca(2+) store depletion. Using fura-based imaging of intracellular Ca(2+) in cultured bag cell neurons, we now characterize this pathway as store-operated Ca(2+) influx. In the absence of extracellular Ca(2+), the endoplasmic reticulum Ca(2+)-ATPase inhibitors, cyclopiazonic acid (CPA) or thapsigargin, depleted intracellular stores and elevated intracellular free Ca(2+). With the subsequent addition of extracellular Ca(2+), a prominent Ca(2+) influx was observed. The ryanodine receptor agonist, chloroethylphenol (CEP), also increased intracellular Ca(2+) but did not initiate store-operated Ca(2+) influx, despite overlap between CEP- and CPA-sensitive stores. Bafilomycin A, a vesicular H(+)-ATPase inhibitor, liberated intracellular Ca(2+) from acidic stores and attenuated subsequent Ca(2+) influx, presumably by replenishing CPA-depleted stores. Store-operated Ca(2+) influx was partially blocked by low concentrations of La(3+) or BTP2, and strongly inhibited by either 1-[b-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole (SKF-96365) or a high concentration of Ni(2+). Regarding IP(3) receptor blockers, 2-aminoethyldiphenyl borate, but not xestospongin C, prevented store-operated Ca(2+) influx. However, jasplakinolide, an actin stabilizer reported to inhibit this pathway in smooth muscle cell lines, was ineffective. The bag cell neurons initiate reproductive behavior through a prolonged afterdischarge associated with intracellular Ca(2+) release and neuropeptide secretion. Store-operated Ca(2+) influx may serve to replenish stores depleted during the afterdischarge or participate in the release of peptide that triggers behavior.