Serotonin-induced changes in membrane potential and cytosolic free calcium in a clonal pituitary cell line (AtT-20) of cultured mouse corticotropes.
The effects of serotonin (5-HT) were examined on the cytosolic free calcium concentration, [Ca2+]i, in fura-2-loaded cells from a clonal cell line derived from the mouse anterior pituitary gland (AtT-20/D16v). Brief applications of 5-HT produced transient increases in [Ca2+]i. The duration and the amplitude of the 5-HT-induced increase in [Ca2+]i depended on the duration of 5-HT application. Longer duration (> 150 msec) applications of 5-HT produced a transient increase followed by a prolonged plateau phase of [Ca2+]i. Oscillations in [Ca2+]i were initiated and maintained in previously quiescent corticotropes following brief exposures to 5-HT. Addition of cobalt (500 microM-3.6 mM) to the extracellular solution abolished oscillations in [Ca2+]i and produced transient but not sustained increases in [Ca2+]i in response to 5-HT. Electrophysiological responses to 5-HT were recorded in separate experiments using the whole-cell patch clamp recording technique. Application of 5-HT to single cells produced a depolarization which was accompanied by a decrease in membrane conductance when measured under voltage clamp. The duration of the depolarizing response also increased with the duration of the 5-HT application. With longer duration 5-HT applications, the 5-HT-induced depolarizing response resembled the spontaneous action potential responses recorded in the same cell. However, the 5-HT-induced depolarizations were unaltered in the presence of extracellular cobalt. This suggests that the transient increase in [Ca2+]i recorded when 5-HT was applied in the presence of cobalt may represent intracellular release of calcium. These results demonstrate that 5-HT activates single cultured corticotropes directly by producing an increase in [Ca2+]i and cell depolarization.
University of Vermont College of Medicine, Department of Anatomy and Neurobiology, Burlington 05405.
J F
JF
Fiekers
L M
LM
Konopka
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002999:Clone Cells; D003600:Cytosol / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D010903:Pituitary Gland, Anterior / Q000378:metabolism* / Q000648:ultrastructure; D012701:Serotonin / Q000502:physiology*
D012701:Serotonin; D000324:Adrenocorticotropic Hormone; D002118:Calcium