Na ionophore 1 eth 227

Double/barreled Ca²⁺-selective and Na⁺-selective microelectrodes were prepared as described previously [26] (link). The Ca²⁺ ionophore II-ETH 129 or the Na⁺ Ionophore I-ETH 227 (both Fluka Sigma-Aldrich, MO, USA) were used to back-fill the Ca²⁺ and Na⁺-selective microelectrodes, respectively. Each ion-selective microelectrode was individually calibrated as described previously [26] (link). After making measurements of intracellular resting Ca²⁺ ([Ca²⁺]_i) and resting Na⁺ concentration ([Na⁺]_i) all microelectrodes were recalibrated, and if the two calibration curves did not agree within 3 mV, data from that microelectrode were discarded.