Affiliation:
1. From the Cardiovascular Division, Departments of Internal Medicine and Physiology, University of Virginia Health Sciences Center, Charlottesville.
Abstract
Abstract
We examined the interaction among changes in pH
i
, [Ca
2+
]
i
, myosin light-chain phosphorylation, and contraction in arterial smooth muscle stimulated by histamine, NH
4
+
, Tris
+
, and/or changes in extracellular pH (pH
o
). We loaded swine carotid medial tissues with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein to measure pH
i
or aequorin to measure [Ca
2+
]
i
. Incubation of tissues in NH
4
+
increased pH
i
, [Ca
2+
]
i
, myosin phosphorylation, and force. Washout of NH
4
+
decreased pH
i
and transiently further increased in [Ca
2+
]
i
and force. Incubation of tissues in a similar concentration of Tris
+
or increasing pH
o
also increased pH
i
; however, there were only modest changes in [Ca
2+
]
i
and force. Increasing extracellular pH coincidentally with washout of NH
4
+
prevented the decrease in pH
i
but did not affect the NH
4
+
washout-induced contraction. These data suggest that NH
4
+
altered [Ca
2+
]
i
and contraction by mechanisms other than its effects on pH
i
. The type of pH buffer did not affect the [Ca
2+
]
i
, myosin phosphorylation, or stress response to histamine stimulation. The time course of changes in pH
i
was much slower than the time course of histamine-induced changes in [Ca
2+
]
i
, myosin phosphorylation, and stress. Addition of 10 mmol/L NH
4
+
concurrently with histamine aborted the histamine-induced decrease in pH
i
and significantly slowed the histamine-induced increase in [Ca
2+
]
i
, myosin phosphorylation, and stress. There was little effect on histamine-induced increases in [Ca
2+
]
i
, myosin phosphorylation, or contraction when three other protocols aborted the histamine-induced decrease in pH
i
. These data show that incubation in NH
4
+
can alter [Ca
2+
]
i
and contraction in both unstimulated and histamine-stimulated smooth muscle. However, these effects were not caused by NH
4
+
-dependent changes in pH
i
. It appears that histamine-induced changes in pH
i
have at most minor effects on [Ca
2+
]
i
and contraction of swine carotid artery.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Cited by
15 articles.
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