The role of the plasma-membrane Ca2+-ATPase in Ca2+homeostasis inSinapis albaroot hairs

✍ Scribed by Hubert H. Felle; Andrzej Tretyn; Gottfried Wagner

• Publisher: Springer-Verlag
• Year: 1992
• Tongue: English
• Weight: 751 KB
• Volume: 188
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00192796

✦ Synopsis

The regulation of cytosolic Ca 2+ has been investigated in growing root-hair cells of Sinapis alba L. with special emphasis on the role of the plasmamembrane Ca 2 +-ATPase. For this purpose, erythrosin B was used to inhibit the Ca2+-ATPase, and the Ca 2+ ionophore A23187 was applied to manipulate cytosolic free [Ca 2 +] which was then measured with Ca 2 +-selective microelectrodes. (i) At 0.01 ~M, A23187 had no effect on the membrane potential but enhanced the Ca 2+ permeability of the plasma membrane. Higher concentrations of this ionophore strongly depolarized the cells, also in the presence of cyanide. (ii) Unexpectedly, A 23187 first caused a decrease in cytosolic Ca 2+ by 0.2 to 0.3 pCa units and a cytosolic acidification by about 0.5 pH units. (iii) The depletion of cytosolic free Ca 2 + spontaneously reversed and became an increase, a process which strongly depended on the external Ca 2+ concentration. (iv) Upon removal of A231s 7, the cytosolic free [Ca 2+] returned to its steady-state level, a process which was inhibited by erythrosin B. We suggest that the first reaction to the intruding Ca z+ is an activation of Ca z+ transporters (e.g. ATPases at the endoplasmic reticulum and the plasma membrane) which rapidly remove Ca 2 + from the cytosol. The two observations that after the addition of A23187, (i) Ca 2+ gradients as steep as -600 mV could be maintained and (ii) the cytosolic pH rapidly and immediately decreased without recovery indicate that the Ca 2 +-exporting plasma-membrane ATPase is physiologically connected to the electrochemical pH gradient, and probably works as an nH+/Ca 2+-ATPase. Based on the finding that the Ca2+-ATPase inhibitor erythrosin B had no effect on cytosolic Ca 2+, but caused a strong Ca 2 + increase after the addion of A23187, we conclude that these cells, at least in the short Abbreviations and symbols.