Positive inotropic effects of calcium sensitizers on normal and failing cardiac myocytes

Calcium sensitizers increase myocardial contractile function without affecting Ca²⁺ homeostasis, which might be beneficial in the treatment of patients with heart failure. However, it remains uncertain whether Ca sensitizers induce quantitatively similar inotropic responses in control and failing hearts. To compare their effects in normal versus failing hearts at the cellular level, shortening mechanics and intracellular calcium ([Ca²⁺]_i) transient were simultaneously measured in the left ventricular myocytes isolated from normal dogs (n = 8) and dogs with rapid pacing-induced heart failure (n = 7). CGP 48506 and EMD 57033 exerted a positive inotropic effect in a dose (0.1-3 μM)-dependent manner in both normal and heart failure myocytes. The percent increase of cell shortening magnitude was comparable between the two groups. CGP 48506 and EMD 57033 did not affect the diastolic cell length and resting [Ca²⁺]_i level. They did not affect the duration of [Ca²⁺]_i transient dynamics. Thus Ca²⁺ sensitizers exerted comparable positive inotropic effects without affecting the rest cell length and rest [Ca²⁺]_i in normal and heart failure myocytes.