Intracellular calcium and hormone secretion in clonal AtT-20/D16-16 anterior pituitary cells.
Intracellular ionized Ca2+ concentration was measured in clonal mouse anterior pituitary tumor cells with the fluorescent Ca2+ indicator Quin-2. In control physiological solution, free cytoplasmic Ca2+ concentration was found to be 139 +/- 11 nM. Replacement of 50 mM NaCl by 50 mM KCl in the extracellular fluid caused a 29 mV depolarization and a 4.2-fold increase in the concentration of free cytoplasmic Ca2+. Under comparable depolarizing conditions, a specific influx of 2.66 nmole of 45Ca2+ per mg protein was detected 1 min after addition of high K+, accompanied by a marked increase in the initial rate of beta-endorphin secretion. In the absence of external Ca2+, depolarization by K+ produced little or no increase in either intracellular free Ca2+ or hormone release. Incubation of AtT-20/D16-16 cells in the secretagogue norepinephrine led to a depolarization accompanied by an increase in spontaneous action potential frequency and a marked elevation in cytosolic Ca2+ concentration. Exposure of cells to somatostatin, an inhibitor of hormone release, led to only transient decreases in burst frequency and no significant reduction in intracellular Ca2+ levels. These results indicate that in addition to intracellular Ca2+, other factors also control secretory activity in AtT-20/D16-16 anterior pituitary cells.
Adler
M
M
Neurotoxicology Branch, US Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland.
Sabol
S L
SL
Busis
N
N
Pant
H C
HC
D000200:Action Potentials / Q000187:drug effects; D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002999:Clone Cells; D003593:Cytoplasm / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008839:Microelectrodes; D009638:Norepinephrine / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D013004:Somatostatin / Q000494:pharmacology; D013997:Time Factors; D001615:beta-Endorphin / Q000378:metabolism*
D000634:Aminoquinolines; D013004:Somatostatin; D001615:beta-Endorphin; C035739:Quin2; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine