[Effect of perfusate ionized calcium on mechanical activity of the rat heart in deep hypothermia].
ABSTRACT Effects of different concentrations of ionized calcium ([Ca2+]) in perfusion fluid and of the heart temperature on the systolic pressure (Psyst), heart rate (Vc) and their product as general index of the heart mechanical activity (HMA) of the rat isovolumetrically contracting isolated heart preparations were examined in condition of retrograde perfusion at constant volume with a modified Krebs-Heseleit buffer. An increase of [Ca2+] from 0.62 to 2.5 mM (mmol/l) in the normothermia (38 degrees C) augments Psyst and HMA. Heart rate does not change. An increase of [Ca2+] from 0.62 to 4.5 mM at 20 degrees C augments Vc and HMA. An increase [Ca2+] at 15-11 degrees C decreases psyst and HMA. [Ca2+] does not affect the temperature of the heart arrest.