Role of Ca(2+)-ATPase in spontaneous oscillations of cytosolic free Ca2+ in GH3 rat pituitary cells.
The relative contribution of voltage-sensitive Ca2+ channels, Ca(2+)-ATPases, and Ca2+ release from intracellular stores to spontaneous oscillations in cytosolic free Ca2+ concentration ([Ca2+]i) observed in secretory cells is not well characterized owing to a lack of specific inhibitors for a novel thapsigargin (Tg)-insensitive Ca(2+)-ATPase expressed in these cells. We show that spontaneous [Ca2+]i oscillations in GH3 cells were unaffected by Ca2+ depletion in inositol-1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores by the treatment of Tg, but could be initiated by application of caffeine. Moreover, we demonstrate for the first time that these spontaneous [Ca2+]i oscillations were highly temperature dependent. Decreasing the temperature from 22 to 17 degrees C resulted in an increase in the frequency, a reduction in the amplitude, and large inhibition of [Ca2+]i oscillations. Furthermore, the rate of ATP-dependent 45Ca2+ uptake into GH3-derived microsomes was greatly reduced at 17 degrees C. The effect of decreased temperatures on extracellular Ca2+ influx was minor because the frequency and amplitude of spontaneous action potentials, which activate L-type Ca2+ channels, was relatively unchanged at 17 degrees C. These results suggest that in GH3 secretory cells, Ca2+ influx via L-type Ca2+ channels initiates spontaneous [Ca2+]i oscillations, which are then maintained by the combined activity of Ca(2+)-ATPase and Ca(2+)-induced Ca2+ release from Tg/IP3-insensitive intracellular stores.
D000818:Animals; D001683:Biological Clocks; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000502:physiology*; D002478:Cells, Cultured; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism*; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism; D010902:Pituitary Gland / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D013696:Temperature; D019789:Tetraethylammonium / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors