title: Mitochondria shape hormonally induced cytoplasmic calcium oscillations and modulate exocytosis.
abstract: Pituitary gonadotropes transduce hormonal input into cytoplasmic calcium ([Ca(2+)](cyt)) oscillations that drive rhythmic exocytosis of gonadotropins. Using Calcium Green-1 and rhod-2 as optical measures of cytoplasmic and mitochondrial free Ca(2+), we show that mitochondria sequester Ca(2+) and tune the frequency of [Ca(2+)](cyt) oscillations in rat gonadotropes. Mitochondria accumulated Ca(2+) rapidly and in phase with elevations of [Ca(2+)](cyt) after GnRH stimulation or membrane depolarization. Inhibiting mitochondrial Ca(2+) uptake by the protonophore CCCP reduced the frequency of GnRH-induced [Ca(2+)](cyt) oscillations or, occasionally, stopped them. Much of the Ca(2+) that entered mitochondria is bound by intramitochondrial Ca(2+) buffering systems. The mitochondrial Ca(2+) binding ratio may be dynamic because [Ca(2+)](mit) appeared to reach a plateau as mitochondrial Ca(2+) accumulation continued. Entry of Ca(2+) into mitochondria was associated with a small drop in the mitochondrial membrane potential. Ca(2+) was extruded from mitochondria more slowly than it entered, and much of this efflux could be blocked by CGP-37157, a selective inhibitor of mitochondrial Na(+)-Ca(2+) exchange. Plasma membrane capacitance changes in response to depolarizing voltage trains were increased when CCCP was added, showing that mitochondria lower the local [Ca(2+)](cyt) near sites that trigger exocytosis. Thus, we demonstrate a central role for mitochondria in a significant physiological response.
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle 98195-7290, USA. kaftan@patchclamp.com
authors.forename: E J
authors.initials: EJ
authors.lastname: Kaftan
authors.forename: T
authors.initials: T
authors.lastname: Xu
authors.forename: R F
authors.initials: RF
authors.lastname: Abercrombie
authors.forename: B
authors.initials: B
authors.lastname: Hille
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002369:Castration; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002998:Clonazepam / Q000031:analogs & derivatives / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism*; D004594:Electrophysiology; D005089:Exocytosis / Q000502:physiology*; D005456:Fluorescent Dyes / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D006575:Heterocyclic Compounds, 3-Ring; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D009930:Organic Chemicals; D010902:Pituitary Gland / Q000737:chemistry; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D013841:Thiazepines / Q000494:pharmacology; D013997:Time Factors
chemical_list: D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D007476:Ionophores; D009930:Organic Chemicals; D019831:Sodium-Calcium Exchanger; D013841:Thiazepines; C068483:rhod-2; C071336:calcium green; D007987:Gonadotropin-Releasing Hormone; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D002998:Clonazepam; C079032:CGP 37157; D002118:Calcium