Capacitative Ca²⁺ entry is graded with degree of intracellular Ca²⁺ store depletion in bovine vascular endothelial cells

Abstract

In endothelial cells, release of Ca2+ from endoplasmic reticulum (ER) Ca2+ stores activates Ca2+ influx via the capacitative Ca2+ entry (CCE) pathway. In cultured bovine pulmonary artery endothelial cells, we investigated the relationship between intracellular Ca2+ store load and CCE activity, as well as the kinetics of CCE activation and deactivation, by simultaneously measuring changes in [Ca2+]i and unidirectional manganese (Mn2+) entry through the CCE pathway. Submaximal concentrations of ATP caused quantal release of Ca2+ from the ER, resulting in a dose‐dependent depletion of Ca2+ stores and acceleration of Mn2+ entry. Mn2+ entry rate, as a measure of CCE activity, was graded with the amount of released Ca2+. Maximal activation of CCE did not require complete store depletion. Slow depletion of the ER by exposure to the ER Ca2+ pump inhibitor cyclopiazonic acid resulted in a delayed activation of CCE, revealing a temporal dissociation between release of Ca2+ from intracellular stores and activation of CCE. During [Ca2+]i oscillations, at frequencies higher than 0·5 spikes min−1, each Ca2+ spike resulted in a progressive acceleration of CCE without leading to oscillations of Ca2+ entry. In contrast, low frequency [Ca2+]i oscillations were paralleled by transient CCE that was activated and deactivated with each Ca2+ spike, resulting in an oscillatory pattern of Ca2+ entry. It is concluded that CCE is a rapidly activating process which is graded with store depletion and becomes fully activated before complete depletion. The duration of CCE activation correlates with the degree of store depletion and the time that is required to refill depleted stores. Overall, a mechanism of graded CCE prevents exhaustion of intracellular Ca2+ reserves and provides an efficient way to respond to variable degrees of intracellular store depletion.

Xestospongin C, a novel blocker of IP3 receptor, attenuates the increase in cytosolic calcium level and degranulation that is induced by antigen in RBL‐2H3 mast cells

“…It has been reported that the activity of CCE inversely correlates with the amount of Ca 2+ in the ER (Sedova et al, 2000). Soon after the application of Ca 2+ , as demonstrated in Figure 5a, the activity of CCE was not changed by the treatment with xestospongin C. This result may indicate that the ER had been equally depleted irrespective of the treatment with xestospongin C. However, xestospongin C inhibited the CCE during the sustained phase of the [Ca 2+ ] i increase.…”

Role of endothelial Ca2+ stores in the regulation of hydraulic conductivity of Rana microvessels in vivo

“…However, it is known that IM stimulates the release of Ca 2ϩ from intracellular stores in endothelial cells, rather than by a direct action on plasma membrane Ca 2ϩ channels, (21) at least in vitro. In cultured bovine pulmonary artery endothelial cells Ca 2ϩ influx was a graded response determined by the degree of Ca 2ϩ store depletion and that maximal Ca 2ϩ influx did not require complete Ca 2ϩ store depletion (29). Furthermore, Ca 2ϩ entry has been shown to be regulated by the degree of store filling in endothelial cells in culture (16).…”

Update on vascular endothelial Ca2+signalling: A tale of ion channels, pumps and transporters

“…As a consequence of the rhythmic interplay between InsP3-induced Ca 2+ release and SERCA-mediated Ca 2+ reuptake, SOCE is not constant during the Ca 2+ train. Accordingly, storesensitive Ca 2+ inflow is activated by the partial depletion of the Ca 2+ pool occurring during each Ca 2+ spike and is then turn off by store replenishment [410,412] . Finally, ECs may display repetitive Ca 2+ oscillations in response to the NAD(P)H oxidase-derived H2O2 that is endogenously produced during the ischemia/reperfusion injury [56,413] .…”

“…Agonist-evoked Ca 2+ oscillations require PLC activation by either GPCRs or TKRs [72,339,404,405,408] . The following InsP3-dependent Ca 2+ mobilization may be amplified by adjacent RyRs via CICR [44,134] and requires Ca 2+ inflow to supply releasable Ca 2+ over time and maintain InsP3R sensitivity to the ligand [72,407,409,410] . Ca 2+ entering through either SOCE or the reverse-mode of NCX is sequestered by SERCA into ER lumen before being released again into the cytosol through the open InsP3Rs [72,134,339,404,405] .…”