Figure 1.

Comparison of caffeine-induced Ca²⁺ transients and forward NCX currents in WT vs KO myocytes. A, [Ca²⁺]_i transients and membrane current (I_NCX) recordings during caffeine application in patch clamped WT (n=8) and KO (n=8) myocytes loaded with fura-2 via the patch pipette. Cells were held at −40 mV and exposed to 5 mmol/L caffeine for 1 sec, using a rapid solution exchanger, to release SR Ca²⁺ stores. In WT, the Ca²⁺ release elicited an inward NCX current, which was absent in 8 of 9 KO myocytes. B, Summary graph showing that resting [Ca²⁺]_i and the peak of the [Ca²⁺]_i transient, and therefore SR Ca²⁺ load, were similar in both groups.