Calcium-activated potassium channel (Gardos channel) in control, 4.2^+/-, 4.2^-/-, and 4.1^-/- mouse erythrocytes. Gardos channel, ChTX (50 nM)-sensitive potassium influx was measured at varying concentrations of extracellular calcium in the presence of A23187. Data are expressed as mean ± SD of 3 separate experiments.