Sulfonylurea receptor ligands modulate stretch-induced ANF secretion in rat atrial myocyte culture

Stretch-induced atrial natriuretic factor (ANF) secretion was studied in cultures of neonate atrial appendage myocytes. Stretch, applied for 40 min by hypotonic swelling, increased the mean area of 44 individually imaged myocytes by 4.8-8.8% (P < 0.0001) at 6 min and by 2.3-6.2% (P < 0.05) at 35 min. Stretch increased immunoreactive ANF release by 42% (P < 0.05) from a baseline of 315 pg/ml. The ATP-sensitive K(+) (K(ATP))-channel blocker tolbutamide (100 micromol/l) increased the stretch-stimulated release to 84% (P < 0.01) over baseline, whereas lower concentrations (1, 10, and 30 micromol/l) had no stimulatory effect. The K(ATP)-channel opener diazoxide (0.1, 1, 10, 30, and 100 micromol/l) inhibited stretch- plus tolbutamide-stimulated ANF release in a concentration-dependent manner, with IC(50) = 2.2 micromol/l, although 100 micromol/l diazoxide did not reduce the increase in mean cell area. The stretch-stimulated K(ATP) current, monitored in 82 whole cell recordings with sulfonylurea receptor (SUR) ligands, was inversely correlated with the stretch-induced ANF release (r(2) = 0.79, P < 0. 0001). In the absence of stretch, the K(ATP) current had no relationship with baseline ANF release, and baseline ANF release was not affected by the K(ATP)-channel modulators. The results show that SUR ligands that open K(ATP) channels inhibit stretch-induced ANF release in atrial myocytes, in correlation with the stretch-activated K(ATP) current. The subcellular site of action of the SUR ligands-plasmalemma or intracellular organelles-remains to be determined.