Figure 4. Diminished sarcoplasmic reticulum (SR) Ca²⁺ load and Ca²⁺ transient in miR-22 transgenic mice.

(A) Representative traces of Ca²⁺ transients from TG-M and WT adult ventricular cardiomyocytes upon 1Hz pacing in 1.8mmol/L, Ca²⁺ Tyrode solution, and (B) after rapid exposure to 10mM caffeine. Note that the sweep velocity was constant and the time scale was identical to data in first panel. (C) Quantification of electrically evoked Ca²⁺ transients, and (E) estimation of SERCA2 activity from time constant of Ca²⁺ transient decline (τ of CaT) in TG-M and WT myocytes. (D) SR Ca²⁺ load response, and (F) NCX activity estimation during caffeine stimulation (τ of caffeine decline) in 0 Na⁺, 0 Ca²⁺ Tyrode solution (n = 3-4 mice). Student t test. *, P<0.05.