Guangxitoxin

The composition (in mM) of normal Tyrode's solution was: CaCl₂, 1.8; NaCl, 135; NaH₂PO₄, 0.33; KCl, 5.4; HEPES, 5; MgCl₂, 0.5; glucose, 16.6; adjusted to pH 7.4 with NaOH. The composition (in mM) of KB solution was: KCl, 55; KOH, 50; KH₂PO₄,70; taurine, 20; L-glutamate, 20; MgCl₂, 3; HEPES, 10; glucose, 18; EGTA, 0.6; adjusted to pH 7.3 with KOH. The composition (in mM) of the pipette solution was: KCl, 25; K-aspartate, 110; NaCl, 5; Mg-ATP, 4; MgCl₂, 2; HEPES, 10; EGTA, 10; adjusted to pH 7.2 with KOH. Nortriptyline was purchased from Sigma Chemical Co. (St. Louis, MO, USA) and dissolved in distilled water. DPO-1 and guangxitoxin were purchased from Tocris Cookson (Ellisville, MO, USA) and dissolved in dimethyl sulfoxide (DMSO).

The standard NT solution contained the following (in mM): NaCl 137, KCl 4.4, CaCl₂ 1.7, MgCl₂ 0.6, glucose 13, HEPES 7, and NaH₂PO₄ 1.1. pH was corrected to 7.4 with NaOH. The whole-cell patch pipette solution contained the following (in mM): K-aspartate 118, KCl 28, EGTA 15, HEPES 10, Mg-ATP 3.8, NaCl 5.2, and MgCl₂ 1.5, buffered to pH 7.25 with KOH. The KB solution contained the following (in mM): KCl 48, KOH 73, KH₂PO₄ 23, L-glutamate 52, HEPES 10, glucose 17, MgCl₂ 3.5, EGTA 3.5, and taurine 17, titrated to pH 7.3 with KOH. Fesoterodine was purchased from APExBIO (Apexbio Technology LLC, Houston, TX, USA) and prepared in dimethyl sulfoxide (DMSO). DPO-1, guangxitoxin, and linopirdine were purchased from Tocris Cookson (Ellisville, MO, USA). linopirdine was dissolved in water, and the others were dissolved in DMSO. The final concentration of DMSO was less than 0.1% volume, and this concentration did not affect either the membrane currents or resting membrane potential.

The NT solution, which is extracellular solution in patch-clamp experiment, had the following composition (in mM): 133 NaCl, 5.2 KCl, 16 glucose, 0.5 NaH₂PO₄, 6 HEPES, 0.6 MgCl₂, and 1.7 CaCl₂ (pH 7.4 adjusted with NaOH). The pipette (internal) solution contained (in mM): 111 K-aspartate, 22 KCl, 9.5 HEPES, 4.4 NaCl, 1.3 MgCl₂, 5 Mg-ATP, and 10 EGTA (pH 7.25 adjusted with KOH). The KB solution contained (in mM): 51 KCl, 68 KOH, 23 KH₂PO₄, 3.2 MgCl₂ 9.5 HEPES, 0.5 EGTA, 17 Taurine, 47 L-glutamate, and 16 Glucose (pH 7.35 adjusted with KOH). DPO-1, guangxitoxin, and linopirdine were purchased from Tocris Cookson (Ellisville, MO, USA) and clozapine was purchased from Sigma Chemical Co. (St. Louis, MO, USA). All drugs were prepared as stock solutions in distilled water or dimethyl sulfoxide (DMSO), and were diluted in daily bath (external) solution. The concentration of DMSO in the final dilution did not exceed 0.1% and did not affect the Kv current at this concentration.