Materials
Nicotine hydrogen tartrate salt (nicotine),nitrendipine,verapamil,ω-agatoxin IVA, cadmium chloride, dimethylsulfoxide (DMSO) were obtained from Sigma Aldrich (St. Louis, MO, USA). Dihydro-β-erythroidine hydrobromide (DHβE) (TOCRIS, Bristol, UK), µ-conotoxinGIIIB (Peptide institute Inc., Osaka, Japan). Drugs were dissolved in distilled water with the exceptions of nitrendipine and verapamil which were dissolved in DMSO. Further dilutions for all drugs were done in Ringer solution. In experiments with drugs which were dissolved in DMSO, the same concentration of DMSO was added to the control solution as was present in the solution with the agent. Finally, the DMSO concentration in the solution did not exceed 0.01%.