Dominant role of mitochondria in calcium homeostasis of single rat pituitary corticotropes.
The rise in cytosolic free Ca2+ concentration ([Ca2+]i) is the major trigger for secretion of ACTH from pituitary corticotropes. To better understand the shaping of the Ca2+ signal in corticotropes, we investigated the mechanisms regulating the depolarization-triggered Ca2+ signal using patch-clamp techniques and indo-1 fluorometry. The rate of cytosolic Ca2+ clearance was unaffected by inhibitors of Na+/Ca2+ exchanger or plasma membrane Ca2+-ATPase (PMCA), slightly slowed by sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor, but dramatically slowed by mitochondrial uncouplers or inhibitor of mitochondrial uniporter. Measurements with rhod-2 revealed that depolarization-triggered increase in mitochondrial Ca2+ concentration. Thus, mitochondria have a dominant role in cytosolic Ca2+ clearance. Using the Mn2+ quench technique, we found the presence of a continuous basal Ca2+ influx in corticotropes. This basal Ca2+ influx was balanced by the combined actions of mitochondrial uniporter and PMCA and SERCA pumps. Inhibition of the mitochondrial uniporter or PMCA or SERCA pumps elevated basal [Ca2+]i. Using membrane capacitance measurement, we found that the change in the shape of the depolarization-triggered Ca2+ signal after mitochondrial inhibition was associated with enhancement of the exocytotic response. Thus, mitochondria have a dominant role in the regulation of Ca2+ signal and exocytosis in corticotropes.
Lee
Andy K
AK
9-70 Medical Sciences Building, Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Tse
Amy
A
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D004594:Electrophysiology; D005089:Exocytosis / Q000502:physiology; D006706:Homeostasis / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000502:physiology*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger / Q000502:physiology; D013997:Time Factors
D019831:Sodium-Calcium Exchanger; D000324:Adrenocorticotropic Hormone; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium