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Mitochondrial Ca2+ activates a cation current in Aplysia bag cell neurons.
J Neurophysiol 2010; 103(3):1543-56JN

Abstract

Ion channels may be gated by Ca(2+) entering from the extracellular space or released from intracellular stores--typically the endoplasmic reticulum. The present study examines how Ca(2+) impacts ion channels in the bag cell neurons of Aplysia californica. These neuroendocrine cells trigger ovulation through an afterdischarge involving Ca(2+) influx from Ca(2+) channels and Ca(2+) release from both the mitochondria and endoplasmic reticulum. Liberating mitochondrial Ca(2+) with the protonophore, carbonyl cyanide-4-trifluoromethoxyphenyl-hydrazone (FCCP), depolarized bag cell neurons, whereas depleting endoplasmic reticulum Ca(2+) with the Ca(2+)-ATPase inhibitor, cyclopiazonic acid, did not. In a concentration-dependent manner, FCCP elicited an inward current associated with an increase in conductance and a linear current/voltage relationship that reversed near -40 mV. The reversal potential was unaffected by changing intracellular Cl(-), but left-shifted when extracellular Ca(2+) was removed and right-shifted when intracellular K(+) was decreased. Strong buffering of intracellular Ca(2+) decreased the current, although the response was not altered by blocking Ca(2+)-dependent proteases. Furthermore, fura imaging demonstrated that FCCP elevated intracellular Ca(2+) with a time course similar to the current itself. Inhibiting either the V-type H(+)-ATPase or the ATP synthetase failed to produce a current, ruling out acidic Ca(2+) stores or disruption of ATP production as mechanisms for the FCCP response. Similarly, any involvement of reactive oxygen species potentially produced by mitochondrial depolarization was mitigated by the fact that dialysis with xanthine/xanthine oxidase did not evoke an inward current. However, both the FCCP-induced current and Ca(2+) elevation were diminished by disabling the mitochondrial permeability transition pore with the alkylating agent, N-ethylmaleimide. The data suggest that mitochondrial Ca(2+) gates a voltage-independent, nonselective cation current with the potential to drive the afterdischarge and contribute to reproduction. Employing Ca(2+) from mitochondria, rather than the more common endoplasmic reticulum, represents a diversification of the mechanisms that influence neuronal activity.

Authors+Show Affiliations

Queen's University, Department of Physiology, Kingston, ON K7L 3N6, Canada.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

20071622

Citation

Hickey, Charlene M., et al. "Mitochondrial Ca2+ Activates a Cation Current in Aplysia Bag Cell Neurons." Journal of Neurophysiology, vol. 103, no. 3, 2010, pp. 1543-56.
Hickey CM, Geiger JE, Groten CJ, et al. Mitochondrial Ca2+ activates a cation current in Aplysia bag cell neurons. J Neurophysiol. 2010;103(3):1543-56.
Hickey, C. M., Geiger, J. E., Groten, C. J., & Magoski, N. S. (2010). Mitochondrial Ca2+ activates a cation current in Aplysia bag cell neurons. Journal of Neurophysiology, 103(3), pp. 1543-56. doi:10.1152/jn.01121.2009.
Hickey CM, et al. Mitochondrial Ca2+ Activates a Cation Current in Aplysia Bag Cell Neurons. J Neurophysiol. 2010;103(3):1543-56. PubMed PMID: 20071622.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Mitochondrial Ca2+ activates a cation current in Aplysia bag cell neurons. AU - Hickey,Charlene M, AU - Geiger,Julia E, AU - Groten,Chris J, AU - Magoski,Neil S, Y1 - 2010/01/13/ PY - 2010/1/15/entrez PY - 2010/1/15/pubmed PY - 2010/6/12/medline SP - 1543 EP - 56 JF - Journal of neurophysiology JO - J. Neurophysiol. VL - 103 IS - 3 N2 - Ion channels may be gated by Ca(2+) entering from the extracellular space or released from intracellular stores--typically the endoplasmic reticulum. The present study examines how Ca(2+) impacts ion channels in the bag cell neurons of Aplysia californica. These neuroendocrine cells trigger ovulation through an afterdischarge involving Ca(2+) influx from Ca(2+) channels and Ca(2+) release from both the mitochondria and endoplasmic reticulum. Liberating mitochondrial Ca(2+) with the protonophore, carbonyl cyanide-4-trifluoromethoxyphenyl-hydrazone (FCCP), depolarized bag cell neurons, whereas depleting endoplasmic reticulum Ca(2+) with the Ca(2+)-ATPase inhibitor, cyclopiazonic acid, did not. In a concentration-dependent manner, FCCP elicited an inward current associated with an increase in conductance and a linear current/voltage relationship that reversed near -40 mV. The reversal potential was unaffected by changing intracellular Cl(-), but left-shifted when extracellular Ca(2+) was removed and right-shifted when intracellular K(+) was decreased. Strong buffering of intracellular Ca(2+) decreased the current, although the response was not altered by blocking Ca(2+)-dependent proteases. Furthermore, fura imaging demonstrated that FCCP elevated intracellular Ca(2+) with a time course similar to the current itself. Inhibiting either the V-type H(+)-ATPase or the ATP synthetase failed to produce a current, ruling out acidic Ca(2+) stores or disruption of ATP production as mechanisms for the FCCP response. Similarly, any involvement of reactive oxygen species potentially produced by mitochondrial depolarization was mitigated by the fact that dialysis with xanthine/xanthine oxidase did not evoke an inward current. However, both the FCCP-induced current and Ca(2+) elevation were diminished by disabling the mitochondrial permeability transition pore with the alkylating agent, N-ethylmaleimide. The data suggest that mitochondrial Ca(2+) gates a voltage-independent, nonselective cation current with the potential to drive the afterdischarge and contribute to reproduction. Employing Ca(2+) from mitochondria, rather than the more common endoplasmic reticulum, represents a diversification of the mechanisms that influence neuronal activity. SN - 1522-1598 UR - https://www.unboundmedicine.com/medline/citation/20071622/Mitochondrial_Ca2+_activates_a_cation_current_in_Aplysia_bag_cell_neurons_ L2 - http://www.physiology.org/doi/full/10.1152/jn.01121.2009?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -