Figure 2.

Simultaneous [Na⁺]_i and Ca²⁺ transient measurements; the effect of ouabain. (A) [Na⁺]_i; (B) Ca²⁺ transients. Representative example in a cell from WT mice. Myocytes dually loaded with SBFI and Fluo-4 were paced at 1 Hz until [Na⁺]_i and Ca²⁺ transients reached steady state (point a). Selective NKA-α2 inhibition (5 µM ouabain) slightly raised [Na⁺]_i and significantly increased Ca²⁺ transients (point b). A higher dose of ouabain (300 μM) was then applied. At this concentration, all NKA-α2 and ∼70% of NKA-α1 are blocked. Both [Na⁺]_i and Ca²⁺ transient amplitude were increased considerably (point c).