pHi, [Ca2+]i, and myosin phosphorylation in histamine- and NH4(+)-induced swine carotid artery contraction.
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)
Chen
X L
XL
Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
Rembold
C M
CM
D000641:Ammonia / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002339:Carotid Arteries / Q000187:drug effects; D005452:Fluoresceins / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009218:Myosins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects*
D005452:Fluoresceins; D000641:Ammonia; D006632:Histamine; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D009218:Myosins; D002118:Calcium