Fig. 3.

OsHKT2;4 expression facilitates Ca²⁺ accumulation in Xenopus oocytes. (A) The hyperpolarized pulses produced the same current in the OsHKT2;4-injected oocytes perfused by different Ca²⁺ salts (Left). But the tail current recorded under voltage steps of 55 to −95 mV following a prepulse at −120 mV was dependent on the anions in the Ca²⁺ salts (Right). The oocytes were perfused with a solution containing (in mM) 185 mannitol and 10 Mes–Tris with 10 CaCl₂, CaI₂, Ca (gluconate)₂, or Ca(NO₃)₂. (B) The current–voltage relationship was deduced from currents recorded by hyperpolarized pulses (Left) or by deactivation protocol (Right), respectively. The oocytes were perfused with a solution containing (in mM) 185 mannitol and 10 Mes–Tris with 5 EGTA–Na₄, 1.8 CaCl₂, or 1.8 CaCl₂ + 5 EGTA. (C) OsHKT2;4-injected oocytes uptake more Ca²⁺ than control oocytes. (Left) The time course of ⁴⁵Ca²⁺ accumulation in oocytes bathed in 1.8 mM CaCl₂. (Right) The concentration-dependent ⁴⁵Ca²⁺ accumulation in the oocytes incubated for 10 min in a solution containing 0, 0.3, 1.8, 5, 10, or 20 mM CaCl₂. (D) The typical traces of the currents recorded by hyperpolarized pulses (i) or the tail currents (ii) in OsHKT2;4-injected oocytes perfused with the solution containing (in mM) 10 CaCl₂ or 10 CaCl₂ + 0.1 NPPB. (iii) The current–voltage relationship was deduced from the tail current recorded from OsHKT2;4-injected oocytes perfused with the same solution containing various inhibitors, including 0.1 mM of DIDS, NFA, NPPB, or tamoxifen. Summarized Ca²⁺ uptake was deduced from results of 50 oocytes/condition repeated in three separate experiments, and the current data are from 10 cells/condition.