Mechanism of the potentiating effect of NH4Cl on vasoconstriction in rat aorta.
1. In medium containing 10 or 20 mM KCl, NH4Cl (10 mM) addition significantly diminished tetraphenylphosphonium bromide (TPP+) uptake in A7r5 vascular smooth muscle cells. 2. Addition of 10 mM NH4Cl significantly potentiated the 45Ca2+ uptake of A7r5 cells in medium containing 20 mM KCl; this increased uptake could be reduced to the basal level by pretreatment with 0.1 microM verapamil. 3. In rat aortic strips, KCl at 10 mM induced a slight contraction, that was greatly potentiated by the simultaneous addition of 10 mM NH4Cl. In this case, also, pretreatment with verapamil (1 microM) completely abolished the NH4Cl-potentiating effect. 4. The results suggest that ammonium ion amplifies the K(+)-induced contraction of rat aorta by facilitating transmembraneous Ca2+ influx through the voltage-dependent calcium channel, which may be due to potentiation of KCl-induced depolarization of the plasma membrane.
Tanaka
H
H
Second Department of Internal Medicine, Hyogo College of Medicine, Japan.
Wakabayashi
I
I
Sakamoto
K
K
Kakishita
E
E
D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D002460:Cell Line; D002478:Cells, Cultured; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology; D051381:Rats; D014661:Vasoconstriction / Q000187:drug effects*
D002132:Calcium Radioisotopes; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D000643:Ammonium Chloride; D002118:Calcium; C013289:tetraphenylphosphonium