Influence of NO and [Ca2+]o on [Ca2+]i homeostasis in rat ventricular cardiomyocytes.

In this study, we explored the effect of NO-induced changes in [Ca2+]i homeostasis in rat ventricular cardiomyocytes through variation in extracellular Ca2+ and application of SNAP (S-nitroso-N-acetyl-D,L-penicillamine) as an NO-donor. The Fura-2 signal dynamics and phalloidin intensity profile of z-disks in rat cardiomyocytes served as endpoints to describe the mechanisms involved in the control of the intracellular Ca2+ levels, depending on the kinetics of distribution of the SNAP-produced NO. The results demonstrated that SNAP caused small phalloidin intensity profile changes between the z-lines in the presence of [Ca2+]o. However, in the absence of [Ca2+]o, SNAP in a concentration of 300 μmol/L induced a significant decrease in the distance between z-lines. This SNAP-induced decrease was reflected as a decrease in the phalloidin fluorescence intensity in the middle of the sarcomere, due to the preferential imaging of greater fluorescence in the bulk of the thin filaments. Based on the Ca2+ fluorescence intensity profile, we could suggest that intracellular Ca2+ is mainly affected by the mechanisms of Ca2+ outflow, rather than the mechanisms of Ca2+ inflow in the presence of NO. Actually, through variation in the electrochemical gradient of Ca2+, we induced mechanisms of faster/slower cytosolic Ca2+ emptying. The obtained data showed that the delay in the cytosolic Ca2+ emptying in the presence of [Ca2+]o is due to the increased electrochemical gradient of Ca2+. [ABSTRACT FROM AUTHOR]