Effect of NH4Cl on the contractility of isolated vascular smooth muscle

Using helical strips of isolated rabbit aortas it was studied the influence of a brief exposure to NH4Cl as well as of the subsequent washout phase. These changes did not affect the resting aortic tension but modified the responsiveness of the strip precontracted by norepinephrine (NE): in the presence of NH4Cl there occurred relaxation, and when ammonia was washed out the strip overcontracted transiently. All this was observed in the absence of external pH (pHe) changes. It is postulated that intracellular (IC) perturbations caused by ammonia led to IC alkalosis which was followed by an IC acidosis when the NH4Cl was removed from the preparation. If this assumption proves to be correct, the IC acid-base status--the intracellular pH (pHi)--could be regarded as a modulator of NE-induced contractility of vascular smooth muscle.