An ion current is the influx and/or efflux of ions through an ion channel. In electrolyte like CuSO4, NaCl, etc. there are +ve and - ve ions( Cu++,SO4--) These are forced to move in definite direction under the effect of external electric field causing electric current, thus in current carriers, ions are + vely and - vely charged. Generally, gases are insulator of electricity but they can be ionised by applying high P.D. at low pressure or by irridating gas by X- rays.