Mutual Antagonism of Calcium Entry by Capacitative and Arachidonic Acid-mediated Calcium Entry Pathways

Abstract

In nonexcitable cells, the predominant mechanism for regulated entry of Ca 2؉ is capacitative calcium entry, whereby depletion of intracellular Ca 2؉ stores signals the activation of plasma membrane calcium channels. A number of other regulated Ca 2؉ entry pathways occur in specific cell types, however, and it is not know to what degree the different pathways interact when present in the same cell. In this study, we have examined the interaction between capacitative calcium entry and arachidonic acid-activated calcium entry, which co-exist in HEK293 cells. These two pathways exhibit mutual antagonism. That is, capacitative calcium entry is potently inhibited by arachidonic acid, and arachidonic acid-activated entry is inhibited by the pre-activation of capacitative calcium entry with thapsigargin. In the latter case, the inhibition does not seem to result from a direct action of thapsigargin, inhibition of endoplasmic reticulum Ca 2؉ pumps, depletion of Ca 2؉ stores, or entry of Ca 2؉ through capacitative calcium entry channels. Rather, it seems that a discrete step in the pathway signaling capacitative calcium entry interacts with and inhibits the arachidonic acid pathway. The findings reveal a novel process of mutual antagonism between two distinct calcium entry pathways. This mutual antagonism may provide an important protective mechanism for the cell, guarding against toxic Ca 2؉ overload.

2-Aminoethoxydiphenyl borate (2-APB) antagonises inositol 1,4,5-trisphosphate-induced calcium release, inhibits calcium pumps and has a use-dependent and slowly reversible action on store-operated calcium entry channels

“…Between recordings, the electrical pacing was maintained, but the UV illumination of Indo1 was removed to prevent photodamage or bleaching of the indicator. donate (data not shown), consistent with observations using HEK-293 cells [32]. Several other non-voltage-activated Ca 2+ entry pathways that are distinct from SOC are also not inhibited by 2-APB, including maitotoxin-evoked Ca 2+ entry in hepatocytes [17], S-nitrosylation-induced influx in a smooth muscle cell line [33], Ca 2+ influx caused by diacylglycerol analogues in PC12 cells [34], muscarinic activation of non-selective cation channels in smooth muscle [35].…”

Reciprocal Regulation of Capacitative and Arachidonate-regulated Noncapacitative Ca2+ Entry Pathways

“…The result is that the transition from an oscillatory [Ca 2ϩ ] i signal to a sustained [Ca 2ϩ ] i signal is associated with a switch in the predominant mode of Ca 2ϩ entry from the ARC channels to the SOC channels, thereby minimizing overall increases in the rate of Ca 2ϩ entry. This inhibition may be related, in part, to the "mutual antagonism" between capacitative and AA-dependent noncapacitative Ca 2ϩ entry recently reported by Luo et al (48). However, these authors were unable to identify the basis for their proposed antagonism, and their conclusions were based on the differential effects of Gd 3ϩ and 2-aminoethyoxydiphenyl borate, agents that are known to have multiple effects on various signaling pathway components and ion channels.…”

Stimulation of arachidonic acid release by vasopressin in A7r5 vascular smooth muscle cells mediated by Ca2+‐stimulated phospholipase A2

“…It is, however, clear that in A7r5 cells, as in many other cells [11][12][13], arachidonic acid (AA) contributes to the coordinate regulation of CCE and NCCE [5,6,14]. In A7r5 cells, the AA that regulates Ca 2+ entry is released from DAG by DAG lipase [5,6], whereas in other cells it is provided by the action of phospholipase A 2 (PLA 2 ) on phospholipids [11,15] or by PLA 2 and DAG lipase [16].…”