Regulation of agonist-evoked [Ca2+]i oscillation by intracellular Ca2+ and Ba2+ in AR42J cells.
Measurements of intracellular Ca2+ ([Ca2+]i) and intracellular Ba2+ ([Ba2+]i) in single AR42J cells were used to evaluate the effect of [Ca2+]i and [Ba2+]i on agonist-evoked [Ca2+]i oscillations. Variations in [Ca2+]i and [Ba2+]i were imposed by gradual activation of entry through voltage-activated Ca2+ channels (VACC) present in the plasma membrane of these cells. Activation of high K+ was followed by partial inactivation of the channels and stabilization of [Ca2+]i at a new steady-state level depending on the extent of depolarization. Activation by BAY K 8644 was followed by complete inactivation and return of [Ca2+]i to resting levels. Ba2+ activated the channels and entered the cells but could not be removed from the cytosol by cellular Ca2+ pumps. The use of channel blockers and the ability to increase [Ca2+]i and [Ba2+]i by channel activation during [Ca2+]i oscillations showed that VACC do not contribute to or are activated during agonist-stimulated Ca2+ oscillation in this cell type. Graded activation of VACC showed that an increase in [Ca2+]i between the spikes to below 200 nM increased the frequency of the oscillation. Further increase in [Ca2+]i caused gradual reduction in the frequency. At [Ca2+]i above 500 nM, [Ca2+]i oscillations were inhibited. The inhibitory but not the stimulatory effects of [Ca2+]i on the oscillations can be mimicked by [Ba2+]i. These observations suggest that [Ca2+]i levels between the spikes play an important role in regulating the oscillations.
Zhang
B X
BX
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235.
Zhao
H
H
Loessberg
P A
PA
Muallem
S
S
D001464:Barium / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002460:Cell Line; D004594:Electrophysiology; D007425:Intracellular Membranes / Q000378:metabolism*; D009994:Osmolar Concentration
D015220:Calcium Channels; D001464:Barium; D002118:Calcium