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 by 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.
- intracellular barium
- intracellular calcium
- voltage-activated calcium channels
ASJC Scopus subject areas
- Cell Biology