Atrial natriuretic factor gene expression in isolated rat hearts subjected to stretch or hypoxia with and without atp-sensitive k channel blocker

Our previous studies show that ATP-sensitive potassium channels (KATP) are potent regulators of atrial natriuretic factor (ANF) release from isolated rat hearts. This study was designed to determine whether short-term stretch, and acute hypoxia in presence or absence of KATP channel blocker regulate ANF gene expression in isolated rat hearts. Six groups of rat hearts were studied: baseline, stretch (increased left atrial pressure, 1.01.5mmHg applied for 12 min), hypoxia (10%O2 in 85%N2+5%CO2 applied for 12 min), tolbutamide (TOLB, a KATP channel blocker, lOOuM), stretch plus TOLB and hypoxia plus TOLB. At 44 min after applying stretch or hypoxia, right and left atrial appendages were frozen in liquid nitrogen for measurement of ANF mRNA by Northern blotting. The ANF mRNA levels of pooled extracts from 5-6 rats were expressed relative to the densitometric absorbence of GAPDH (glyceraldehyde phosphate dehydrogenase) mRNA. The Northern blotting analysis demonstrated a two-fold increase of ANF mRNA in acute hypoxia-treated appendages compared to baseline. TOLB did not affect ANF mRNA expression induced by hypoxia. Stretch caused an increase of ANF mRNA expression, which was potentiated by tolbutamide TOLB alone did not influence basal ANF mRNA levels.The preliminary results suggest that acute hypoxia can induce an early response of ANF mRNA expression, and cardiac myocyte KATP channels may be involved in the regulation of ANF biosynthesis induced by short-term stretch. Supported by NIH grant RO1 HL40553 and grants VA-94-F-38 and VA-94-G-25 from AHA.