Involvement of mitochondria in intracellular calcium sequestration by rat gonadotropes.
Intracellular Ca2+ ([Ca2+]i) dynamics were studied in identified rat gonadotropes using the whole-cell patch-clamp technique in conjunction with Indo-1 photometry. The kinetics of depolarization-induced [Ca2+]i transients vary with Ca2+ load. In addition to a rapid initial decay, large (> 500 nM) [Ca2+]i transients have a slow plateau phase. Application of the mitochondrial inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP) significantly slows the decay of [Ca2+]i transients, consistent with stopping uptake of Ca2+ by mitochondria. CCCP causes a small increase of [Ca2+]i at rest. After a large Ca2+ entry the amount is much larger, consistent with release from a mitochondrial Ca2+ pool that fills during cytoplasmic Ca2+ loading. The rate of Ca2+ uptake by mitochondria is dependent upon [Ca2+]i. Consistent with previous studies, gonadotropin releasing hormone (GnRH) induces [Ca2+]i oscillations. The mitochondrial inhibitors CCCP and cyanide (CN-) terminate these oscillations. The mitochondrial ATP-synthase inhibitor oligomycin reduces the frequency and increases the amplitude of the oscillations. In the presence of ruthenium red (a non-specific blocker of the mitochondrial Ca(2+)-uniporter) in the pipette, GnRH does not induce rhythmic [Ca2+]i oscillations. We suggest that mitochondria play a significant role in the rapid clearance of cytosolic Ca2+ loads in gonadotropes and participate in GnRH-induced periodic [Ca2+]i oscillations.
Hehl
S
S
Department of Physiology and Biophysics, University of Washington, Seattle 98195-7290, USA.
Golard
A
A
Hille
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002478:Cells, Cultured / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000201:enzymology; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009919:Orchiectomy; D018408:Patch-Clamp Techniques; D010902:Pituitary Gland / Q000166:cytology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014475:Uncoupling Agents / Q000494:pharmacology
D014475:Uncoupling Agents; D007987:Gonadotropin-Releasing Hormone; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000252:Calcium-Transporting ATPases; D002118:Calcium