Figure 4

Acute stimulation with 5 nM NRG1 induces [Ca²⁺] _i increases in ErbB4-transfected cells. ErbB4-transfected cells were loaded with 3 μM FURA-2-AM and perfused with a Tyrode Standard solution with or without calcium in the presence of 5 nM NRG1 in order to characterize the [Ca²⁺]_i changes induced by the factor. A: Mean ± SE from a representative experiment (n = 75), showing calcium induced by 5 nM NRG1 in the presence of 2 mM extracellular [Ca²⁺]. B: Example of a response to 5 nM NRG1 in the absence of extracellular Ca²⁺ (0Ca). NRG1 induced a slow increase due to release from intracellular stores; reintroduction of 2 mM [Ca²⁺] in the external bath induced a sustained increase of [Ca²⁺]_i (arrow). C: Lack of response to NRG1 in cells in which intracellular stores had been depleted by means of 0.1 mM thapsigargin (TG). Mean ± SE from a representative experiment (n = 19). D: Histogram representing mean values of maximum amplitude (ΔR) responses to NRG1 in Tyrode Standard solution and in the same solution without Ca²⁺ (n = 164 in Tyrode solution without Ca²⁺ ; 119 in Tyrode Standard). Data represent means + SE from three independent experiments. *** p < 0.001 vs NRG1-Tyr.