The effect of the ionic composition of bathing solution on the potency of apamin.

<p>Representative recordings of K_Ca2 current in HEK 293 cells transiently transfected with K_Ca2.2. The recordings were made in standard solution (A), nominally Ca ²⁺ and Mg²⁺ free solution (B) and Na⁺, Mg²⁺ and Ca²⁺ free solution in which NaCl was replaced by 280 mM sucrose (C). In each case the left panel shows currents recorded before and the right panel after the application of 100 pM apamin. D Summary of data for the inhibition caused by 100 pM apamin in the solutions used in A, B and C. Vertical bars show s.e.m. * denotes that the values were significantly different from the effect of apamin in standard solution (p<0.05, unpaired t-test). E Concentration-inhibition curve for apamin applied in Ca²⁺ and Mg²⁺ free solution. Each point is the mean of 3–5 observations with vertical bars indicating s.e.m. The solid line was drawn from a fit of the Hill equation with IC₅₀ = 20±3 pM and <i>n</i> = 0.8±0.06. The dashed line represents the concentration-inhibition curve for apamin in standard solution shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073328#pone-0073328-g004" target="_blank">Figure 4</a>.