Effect of Extracellular Calcium Depletion on Atrial Natriuretic Factor Secretion and Gene Expression

Extracellular ca2+ concentration ([ca2+]o) may be one of the factors affecting atrialnatriuretic factor (anf) release. in the previous studies, there are opposite reportsabout the effect of [ca2+]o on anf secretion. therefore, the effect of [ca2+]odepletion 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 andabsence of [ca2+]o, and anf secretion were measured using radioimmunoassaymethod. cyclohexamide was used in another group as a protein synthesis inhibitor.anf mrna level in atria measured by real time pcr. [ca2+]o depletion induceda 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 synthesisinhibition by cyclohexamide did not abolish or significantly decrease the stimulatoryeffect of ca2+-free media on anf secretion. the anf gene expression was notsignificantly affected by ca2+-free media. these results suggest that the contractileand endocrine function of atrial cardiocytes are differently affected by [ca2+]o andmay represent an adaptation to the dual roles of the atrial myocytes contraction andsecretion.