Figure 1. Effect of GDF-15 on [Ca²⁺]_i induced by high K⁺ in rat CGNs.

(A) Intracellular Ca²⁺ imaging of control and GDF-15-treated CGNs before (Base) and after (HK) depolarization by acute perfusion with 27 mM K⁺. Changes in fura 2 fluorescence excitation ratios with increasing [Ca²⁺]_i are depicted as a colour gradient from purple to red. Scale bar, 50 μm. (B) Changes in [Ca²⁺]_i upon application of a depolarizing stimulus, as measured by quantification of fluorescence excitation ratios. The arrow represents a 30-s perfusion with a depolarizing solution of 27 mM K⁺. (C) Statistical analysis of [Ca²⁺]_i induced by high K⁺ in the presence or absence of GDF-15. Results are means±S.E.M. *P<0.05 for the two groups connected with a straight line. Ctrl, control.