Na+-Dependent Ca2+ Transport Modulates the Secretory Response to the Fcϵ Receptor Stimulus of Mast Cells

Abstract

Immunological stimulation of rat mucosal-type mast cells (RBL-2H3 line) by clustering of their Fcepsilon receptors (FcepsilonRI) causes a rapid and transient increase in free cytoplasmic Ca(2+) ion concentration ([Ca(2+)](i)) because of its release from intracellular stores. This is followed by a sustained elevated [Ca(2+)](i), which is attained by Ca(2+) influx. Because an FcepsilonRI-induced increase in the membrane permeability for Na(+) ions has also been observed, and secretion is at least partially inhibited by lowering of extracellular sodium ion concentrations ([Na(+)](o)), the operation of a Na(+)/Ca(2+) exchanger has been considered. We found significant coupling between the Ca(2+) and Na(+) ion gradients across plasma membranes of RBL-2H3 cells, which we investigated employing (23)Na-NMR, (45)Ca(2+), (85)Sr(2+), and the Ca(2+)-sensitive fluorescent probe indo-1. The reduction in extracellular Ca(2+) concentrations ([Ca(2+)](o)) provoked a [Na(+)](i) increase, and a decrease in [Na(+)](o) results in a Ca(2+) influx as well as an increase in [Ca(2+)](i). Mediator secretion assays, monitoring the released beta-hexosaminidase activity, showed in the presence of extracellular sodium a sigmoidal dependence on [Ca(2+)](o). However, the secretion was not affected by varying [Ca(2+)](o) as [Na(+)](o) was lowered to 0.4 mM, while it was almost completely inhibited at [Na(+)](o) = 136 mM and [Ca(2+)](o) < 0.05 mM. Increasing [Na(+)](o) caused the secretion to reach a minimum at [Na(+)](o) = 20 mM, followed by a steady increase to its maximum value at 136 mM. A parallel [Na(+)](o) dependence of the Ca(2+) fluxes was observed: Antigen stimulation at [Na(+)](o) = 136 mM caused a pronounced Ca(2+) influx. At [Na(+)](o) = 17 mM only a slight Ca(2+) efflux was detected, whereas at [Na(+)](o) = 0.4 mM no Ca(2+) transport across the cell membrane could be observed. Our results clearly indicate that the [Na(+)](o) dependence of the secretory response to FcepsilonRI stimulation is due to its influence on the [Ca(2+)](i), which is mediated by a Na(+)-dependent Ca(2+) transport.

Up‐regulation of activated macrophages in response to degeneration in the taste system: Effects of dietary sodium restriction

“…Functionally impaired ED1 ϩ cells may be unable to migrate to damaged tissue. Indeed, altering the concentration of extracellular sodium can change both sodium and calcium gradients across the leukocyte membrane, which may perturb monocyte and/or macrophage functions, such as cytokine gene expression, cellular proliferation, and secretory responses (Kerschbaum and Cahalan, 1999;Rumpel et al, 2000;Janeway et al, 2001).…”

Regulation of Ca2+ Signaling with Particular Focus on Mast Cells

“…This also appears to be true for endogenous Na + /Ca 2+ exchangers in mast cells where significant coupling of Na + and Ca 2+ plasma gradients has been observed 181,182. The effects of varying the concentrations of external Na + on the influx of Ca 2+ or Sr 2+ , changes in [Ca 2+ ] i , and mast cell degranulation suggest that these events are tightly coupled 182. Whole-cell patch clamp recordings indicate that mast cells express both K + -dependent and K + -independent Na + /Ca 2+ exchangers (identified as NCKX3, NCKX1, and NCX3), which may account for as much as 50% of the Ca 2+ extruded from cells once [Ca 2+ ] i reaches 200 nM 178.…”

“…When activated by store depletion, the exogenous exchangers modulate localized and global changes in cellular Ca 2+ levels 179,180. This also appears to be true for endogenous Na + /Ca 2+ exchangers in mast cells where significant coupling of Na + and Ca 2+ plasma gradients has been observed 181,182. The effects of varying the concentrations of external Na + on the influx of Ca 2+ or Sr 2+ , changes in [Ca 2+ ] i , and mast cell degranulation suggest that these events are tightly coupled 182.…”

Expression and function of Na+/Ca2+ exchangers 1 and 3 in human macrophages and monocytes

“…Interestingly, preliminary studies in murine macrophages [14] and human basophils [15] have suggested the presence of NCX in immune cells. NCX activities have also been reported in human lymphocytes [16], neutrophils [17], and rat mast cells [18,19] investigated using pharmacological agents. In these cells, NCX may contribute either to the extrusion of Ca 21 after Ca 21 -spiking events or to the increase in [Ca 21 ] i during cell activation.…”