Chen X L, Rembold C M
Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
Hypertension. 1995 Apr;25(4 Pt 1):482-9. doi: 10.1161/01.hyp.25.4.482.
We examined the interaction among changes in pHi, [Ca2+]i, myosin light-chain phosphorylation, and contraction in arterial smooth muscle stimulated by histamine, NH4+, Tris+, and/or changes in extracellular pH (pHo). We loaded swine carotid medial tissues with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein to measure pHi or aequorin to measure [Ca2+]i. Incubation of tissues in NH4+ increased pHi, [Ca2+]i, myosin phosphorylation, and force. Washout of NH4+ decreased pHi and transiently further increased in [Ca2+]i and force. Incubation of tissues in a similar concentration of Tris+ or increasing pHo also increased pHi; however, there were only modest changes in [Ca2+]i and force. Increasing extracellular pH coincidentally with washout of NH4+ prevented the decrease in pHi but did not affect the NH4+ washout-induced contraction. These data suggest that NH4+ altered [Ca2+]i and contraction by mechanisms other than its effects on pHi. The type of pH buffer did not affect the [Ca2+]i, myosin phosphorylation, or stress response to histamine stimulation. The time course of changes in pHi was much slower than the time course of histamine-induced changes in [Ca2+]i, myosin phosphorylation, and stress. Addition of 10 mmol/L NH4+ concurrently with histamine aborted the histamine-induced decrease in pHi and significantly slowed the histamine-induced increase in [Ca2+]i, myosin phosphorylation, and stress. There was little effect on histamine-induced increases in [Ca2+]i, myosin phosphorylation, or contraction when three other protocols aborted the histamine-induced decrease in pHi. These data show that incubation in NH4+ can alter [Ca2+]i and contraction in both unstimulated and histamine-stimulated smooth muscle. However, these effects were not caused by NH4(+)-dependent changes in pHi.(ABSTRACT TRUNCATED AT 250 WORDS)
我们研究了在组胺、NH₄⁺、Tris⁺刺激和/或细胞外pH（pHo）变化时，动脉平滑肌中细胞内pH（pHi）变化、细胞内钙浓度（[Ca²⁺]i）、肌球蛋白轻链磷酸化和收缩之间的相互作用。我们用2',7'-双（2-羧乙基）-5（6）-羧基荧光素加载猪颈动脉中膜组织以测量pHi，或用水母发光蛋白测量[Ca²⁺]i。将组织置于NH₄⁺中孵育会增加pHi、[Ca²⁺]i、肌球蛋白磷酸化和张力。洗脱NH₄⁺会降低pHi，并使[Ca²⁺]i和张力短暂进一步增加。将组织置于相似浓度的Tris⁺中孵育或提高pHo也会增加pHi；然而，[Ca²⁺]i和张力仅有适度变化。在洗脱NH₄⁺的同时提高细胞外pH可防止pHi降低，但不影响NH₄⁺洗脱诱导的收缩。这些数据表明，NH₄⁺改变[Ca²⁺]i和收缩的机制并非通过其对pHi的影响。pH缓冲剂的类型不影响[Ca²⁺]i、肌球蛋白磷酸化或对组胺刺激的应激反应。pHi变化的时间进程比组胺诱导的[Ca²⁺]i、肌球蛋白磷酸化和应激变化的时间进程慢得多。与组胺同时添加10 mmol/L NH₄⁺可消除组胺诱导的pHi降低，并显著减缓组胺诱导的[Ca²⁺]i、肌球蛋白磷酸化和应激增加。当其他三种方案消除组胺诱导的pHi降低时，对组胺诱导的[Ca²⁺]i、肌球蛋白磷酸化或收缩几乎没有影响。这些数据表明，在NH₄⁺中孵育可改变未刺激和组胺刺激的平滑肌中的[Ca²⁺]i和收缩。然而，这些作用并非由NH₄⁺依赖性的pHi变化引起。（摘要截断于250字）
