Mechanism of the potentiating effect of NH4Cl on vasoconstriction in rat aorta

1. 1. In medium containing 10 or 20 mM KCI, NH 4 Cl (10 mM) addition significantly diminished tetraphenylphosphonium bromide (TPP + ) uptake in A7r5 vascular smooth muscle cells. 2. 2. Addition of 10 mM NH 4 Cl significantly potentiated the 45 Ca 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 4 C1. In this case, also, pretreatment with verapamil (1 μM) completely abolished the NH 4 C1-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.