Ouabain at 100 microM stimulated ANP secretion in paced rat atria, an effect completely inhibited by lanthanum and partially inhibited by ryanodine (47%) and HMA (71%).
Ouabain stimulates ANP secretion in rat atria through mechanisms dependent on calcium influx, sarcoplasmic reticulum calcium release, and Na(+)-H+ exchange.
Ouabain increases atrial natriuretic peptide (ANP) secretion. When isolated superfused rat left atria were paced at 2 Hz, ouabain at concentrations of 50, 100, and 200 microM increased ANP secretion by 2.0 +/- 0.3-, 3.2 +/- 0.5-, and 4.2 +/- 0.5-fold, respectively. In this study, we examine the mechanism of ouabain-stimulated ANP secretion using the dose of 100 microM. To determine whether calcium played a role, atria were superfused with the calcium antagonist lanthanum. Superfusion with 2 mM LaCl3 completely inhibited ouabain-stimulated secretion, suggesting that calcium influx and/or sarcoplasmic reticulum (SR) calcium release provide essential sources of calcium for the stimulatory pathway. To determine the contribution of calcium from the SR, atria were superfused with ryanodine, an agent that depletes the SR of calcium. Superfusion with 1 microM ryanodine inhibited ouabain-stimulated secretion by 47%. Inhibition of Na+,K(+)-ATPase allows sodium to accumulate in the cell. A rise in intracellular sodium alters Na(+)-Ca2+ exchange, leading to an increase in cytosolic calcium. To determine the mechanism of sodium entry, atria were superfused with 5-(N,N-hexamethylene)amiloride (HMA), an inhibitor of Na(+)-H+ exchange, or with bumetanide, an inhibitor of Na(+)-K(+)-Cl- cotransport. Superfusion with 25 microM HMA inhibited ouabain-stimulated secretion by 71%; however, 100 microM bumetanide had no significant effect on secretion. Ouabain failed to stimulate ANP secretion by nonpaced (nonbeating) atria. Likewise, superfusion with the combination of ryanodine (1 microM) and the calcium channel antagonist israpidine (10 microM) totally blocked ouabain-stimulated ANP secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
SCHIEBINGER et al. (Sat,) conducted a other in Atrial natriuretic peptide secretion mechanism. Ouabain vs. Various inhibitors (LaCl3, ryanodine, HMA, bumetanide, israpidine) was evaluated on Atrial natriuretic peptide (ANP) secretion. Ouabain at 100 microM stimulated ANP secretion in paced rat atria, an effect completely inhibited by lanthanum and partially inhibited by ryanodine (47%) and HMA (71%).