Effects of cigarette smoke extract (CSE) on the contraction, spontaneous beating rate and intracellular Ca<sup>2+</sup> dynamics in adult and neonatal cardiomyocytes

Smoking is a known risk factor of ischemic heart diseases via various toxic effects on several tissues, including lung and cardiovascular systems. However, the direct effects of smoking substances on the cardiomyocyte function and its cellular mechanism have not been fully clarified. In the present study, we examined the effects of CSE on the contractile function and intracellular Ca2+ transients using freshly isolated adult and cultured neonatal cardiomyocytes. These parameters were analyzed using the Cell Motion Imaging System (Sony SI8000). Application of 1% CSE significantly increased the spontaneous beating rate of cultured neonatal cardiomyocytes. On the other hand, the same treatment decreased the cell shortening of electrically stimulated adult cardiomyocytes. Intracellular Ca2+ transients obtained from Fluo-8-loaded cardiomyocytes showed that 1% CSE induced massive increase in diastolic Ca2+ levels, little change in systolic levels, and as a result, significant decrease in Ca2+ transient amplitude. These results suggest that CSE weaken the contractile function of cardiomyocytes by altering intracellular Ca2+ dynamics, while increasing in the beating rate. Further cellular mechanisms, such as the possibility of Ca2+ leak from the sarcoplasmic reticulum and change in the myofilament Ca2+ sensitivity, would be discussed.