Mechanism of the potentiating effect of NH 4Cl on vasoconstriction in rat aorta

Abstract

1. 1. In medium containing 10 or 20 mM KCI, NH 4Cl (10 mM) addition significantly diminished tetraphenylphosphonium bromide (TPP +) uptake in A7r5 vascular smooth muscle cells. 2. 2. Addition of 10 mM NH 4Cl significantly potentiated the 45Ca 2+ uptake of A7r5 cells in medium containing 20 mM KCI; this increased uptake could be reduced to the basal level by pretreatment with 0.1 μM verapamil. 3. 3. In rat aortic strips, KCI at 10 mM induced a slight contraction, that was greatly potentiated by the simultaneous addition of 10 mM NH 4C1. In this case, also, pretreatment with verapamil (1 μM) completely abolished the NH 4C1-potentiating effect. 4. 4. The results suggest that ammonium ion amplifies the K +-induced contraction of rat aorta by facilitating transmembraneous Ca 2+ influx through the voltage-dependent calcium channel, which may be due to potentiation of KC1-induced depolarization of the plasma membrane.