A Store-Operated Ca Influx Pathway in the Bag Cell Neurons of Aplysia

Kachoei, Babak A., Ronald J. Knox, Didier Uthuza, Simon Levy, Leonard K. Kaczmarek, and Neil S. Magoski. A store-operated Ca influx pathway in the bag cell neurons of Aplysia. J Neurophysiol 96: 2688–2698, 2006. First published August 2, 2006; doi:10.1152/jn.00118.2006. Although store-operated Ca 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 entry pathway can be activated by Ca store depletion. Using fura-based imaging of intracellular Ca in cultured bag cell neurons, we now characterize this pathway as store-operated Ca influx. In the absence of extracellular Ca , the endoplasmic reticulum Ca -ATPase inhibitors, cyclopiazonic acid (CPA) or thapsigargin, depleted intracellular stores and elevated intracellular free Ca . With the subsequent addition of extracellular Ca , a prominent Ca influx was observed. The ryanodine receptor agonist, chloroethylphenol (CEP), also increased intracellular Ca but did not initiate store-operated Ca influx, despite overlap between CEPand CPA-sensitive stores. Bafilomycin A, a vesicular H -ATPase inhibitor, liberated intracellular Ca from acidic stores and attenuated subsequent Ca influx, presumably by replenishing CPA-depleted stores. Store-operated Ca influx was partially blocked by low concentrations of La or BTP2, and strongly inhibited by either 1-[b-[3-(4-methoxyphenyl)propoxy]-4methoxyphenethyl]-1H-imidazole (SKF-96365) or a high concentration of Ni . Regarding IP3 receptor blockers, 2-aminoethyldiphenyl borate, but not xestospongin C, prevented store-operated Ca 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 release and neuropeptide secretion. Store-operated Ca influx may serve to replenish stores depleted during the afterdischarge or participate in the release of peptide that triggers behavior.