Intracellular Zn2+ Release Modulates Cardiac Ryanodine Receptor Function and Cellular Activity

Several Ca2+-binding proteins bind also Zn2+, suggesting that Zn2+ can modulate the structure and function of many proteins involved in heart function. We first investigated intracellular Zn2+ homeostasis and its possible role in cardiac excitation-contraction (EC)-coupling by using confocal microscopy in adult rat cardiomyocytes loaded with either Zn2+- or Ca2+-specific dye, FluoZin-3 or Fluo-3, respectively. The local ionic releases (sparks) recorded in FluoZin-3 loaded cells were significantly smaller, shorter and less frequent than those of the Fluo-3 loaded cells under control resting conditions. Following 1-μM zinc-pyrithione exposure, the amplitude of the FluoZin-3 sparks increased by 35% leaving Ca2+-sparks unaffected, and a 10-mV leftward shift was observed in the L-type Ca2+-current (ICa)-voltage relation without significant effect on maximal ICa density. Applications of either caffeine or ryanodine, and either a mitochondrial (MT) protonophore or a MT complex I inhibitor suggested that both sarcoplasmic reticulum and mitochondria are intracellular Zn2+ pools. Our western-blot data further showed that there are correlations between the intracellular Zn2+ level and the hyperphosphorylation levels of RyR2 and CAMKII as well as with total PKC activity. Additionally, hyperphosphorylation levels of both ERK-1 and NF-κB also showed a strong dependency on internal Zn2+-level. In conclusion, intracellular Zn2+ might have an important role in the regulation of heart function including transcription and gene expression, implying that intracellular Zn2+ not only has a role in EC-coupling but it is also a major intracellular second messenger in cardiomyocytes.(Supported by TUBITAK SBAG-107S427&SBAG-107S304)