Figure 3.

Increase of intracellular calcium induced by HA through activation of H₁R. (A-D) Representative trace from responsive NPC to 100 μM HA, showing the average ratio (R) of fluorescence of Fura-2 alternating excitation between 340 nm (F₃₄₀) and 380 nm (F₃₈₀) as a measure of [Ca²⁺]_i. HA addition elicited a clear increase (A) that was blocked by co-incubation of HA with the H₁R antagonist chlorpheniramine (Chlorph.) (B), (C) HA added in a medium without extracellular calcium caused a discrete [Ca²⁺]_i rise. (D) Cimetidine (Cimet.) did not block the Ca²⁺ elevation caused by HA. Note that neither chlorpheniramine nor cimetidine modified basal Ca²⁺ levels. (E-P) Representative images from the same experiment in A to D at different times: before the stimulus (E, H, K, N), after HA addition (F, I, L, O) and 80 seconds after the stimulus was given (G, J, M, P). Chlorpheniramine and cimetidine were incubated during the five minutes prior to HA addition. The bar on the side of image E indicates the scale for R = F₃₄₀ / F₃₈₀. (Q) Average values of ratiometric Fura-2 measurements, expressed as a percentage of the basal (before stimulus) value are presented in the graph as the mean ± standard error from three to five independent experiments. ***P <0.0001 versus 100 μM HA and also versus 100 μM HA + Cimet.; ^aP <0.01 versus 100 μM HA without extracellular Ca²⁺. HA, histamine; H₁R, histamine receptor type 1; NPC, neural precursor cells.