effect of extracellular calcium depletion on atrial natriuretic factor secretion and gene expression

extracellular ca 2+ concentration ([ca2+]o) may be one of the factors affecting atrial natriuretic factor (anf) release. in the previous studies, there are opposite reports about the effect of [ca2+]o on anf secretion. therefore, the effect of [ca2+]o depletion on anf secretion and gene expression was studied in the present research. isolated right atria from rats were perfused for 6 and 2 hours in the presence and absence of [ca2+]o, and anf secretion were measured using radioimmunoassay method. cyclohexamide was used in another group as a protein synthesis inhibitor.        anf mrna level in atria measured by real time pcr. [ca 2+]o depletion induced a significant increase in basal anf release. this stimulatory effect peaked at 2 h, then started to decrease and reached around basal levels by 6 h. protein synthesis inhibition by cyclohexamide did not abolish or significantly decrease the stimulatory effect of ca 2+-free media on anf secretion. the anf gene expression was not significantly affected by ca 2+-free media. these results suggest that the contractile and endocrine function of atrial cardiocytes are differently affected by [ca2+]o and may represent an adaptation to the dual roles of the atrial myocytes contraction and secretion.