Figure 4. OMP facilitates NCX activity.

A, The activity of NCX was probed in reverse mode by monitoring the rise of Ca²⁺ _i in response to a stepwise reduction of Na⁺ _o (by substituting Na⁺ by Li⁺). Ca²⁺ responses are reversibly inhibited by the NCX inhibitor KB-R7943 (10 µM) as well as by dichlorobenzamil (DCB, 10 µM). This confirms that the rise in Ca²⁺ induced by low Na⁺ _o is a result of Ca²⁺ entry through NCX. B, Bar histogram of the Ca²⁺ responses obtained after treatment with pharmacological agents that modulate NCX activity. Concentrations are given below each bar (in µM). Number of knobs tested are indicated in parentheses above each bar. C, Averaged Ca²⁺ responses due to reverse mode activity of NCX from WT (gray) and OMP^−/− knobs (black) show a 2.5-fold increase (p<0.0001) in time-to-peak in OMP^−/− (n = 27; N = 5) vs. WT mice (n = 26; N = 4). D, Averaged decay time courses of the same signal in WT (gray) and OMP^−/− knobs (black) reveal an approximately 2-fold increase in the recovery rate in OMP^−/− mice (p<0.03). Data were normalized to the value obtained immediately at the end of the 20-s low Na⁺ stimulus.