Dependence of the resting [Ca2+]cyt of RBL-1 cells on Ca2+ entry

The cytoplasmic Ca2+concentration ([Ca2+]cyt) in resting cells is an equilibrium between several influx and efflux mechanisms. Here we address the question of whether capacitative Ca2+ entry to some extent is active at resting conditions and therefore is part of processes that guarantee a constant [Ca2+]cyt. We measured changes of [Ca2+]cyt in RBL-1 cells with fluorometric techniques. An increase of the extracellular [Ca2+] from 1.3 mM to 5 mM induced an increase in [Ca2+]cyt from 105 +/- 10 nM to 145 +/- 8.5 nM. This increase could be inhibited by 10 microM Gd3+, 10 microM La3+ or 50 microM 2-aminoethoxydiphenyl borate, blockers of capacitative Ca2+ entry. Application of those blockers to a resting cell in a standard extracellular solution (1.3 mM Ca2+) resulted in a decrease of [Ca2+]cyt from 105 +/- 10 nM to 88.5 +/- 10 nM with La3+, from 103 +/- 12 to 89 +/- 12 nM with Gd3+ and from 102 +/- 12 nM to 89.5 +/- 5 nM with 2-aminoethoxydiphenyl borate. From these data, we conclude that capacitative Ca2+ entry beside its function in Ca2+ signaling contributes to the regulation of resting [Ca2+]cyt.