Article date: July 1997
By: Nobutaka Yamakawa, Masuo Ohhashi, Shiro Waga, Takeo Itoh, in Volume 121, Issue 7, pages 1315-1322
The characteristic features of the endothelium‐mediated regulation of the electrical and mechanical activity of the smooth muscle cells of cerebral arteries were studied by measuring membrane potential and isometric force in endothelium‐intact and ‐denuded strips taken from the rabbit middle cerebral artery (MCA).
In endothelium‐intact strips, histamine (His, 3–10 μM) and high K+ (20–80 mM) concentration‐dependently produced a transient contraction followed by a sustained contraction. Noradrenaline (10 μM), 5‐hydroxytryptamine (10 μM) and 9,11‐epithio‐11, 12‐methano‐thromboxane A2 (10 nM) each produced only a small contraction (less than 5% of the maximum K+‐induced contraction).
NG‐nitro‐L‐arginine (L‐NOARG, 100 μM), but not indomethacin (10 μM), greatly enhanced the phasic and the tonic contractions induced by His (1–10 μM) in endothelium‐intact, but not in endothelium‐denuded strips, suggesting that spontaneous or basal release of nitric oxide (NO) from endothelial cells potently attenuates the His‐induced contractions. Acetylcholine (ACh, 0.3–3 μM) caused concentration‐dependent relaxation (maximum relaxation by 89.7±7.5%, n=4, P<0.05) when applied to endothelium‐intact strips precontracted with His. L‐NOARG had little effect on this ACh‐induced relaxation (n=4; P<0.05). Apamin (0.1 μM), but not glibenclamide (3 μM), abolished the relaxation induced by ACh (0.3–3 μM) in L‐NOARG‐treated strips (n=4, P<0.05).
In endothelium‐intact tissues, His (3 μM) depolarized the smooth muscle membrane potential (by 4.4±1.8 mV, n=12, P<0.05) whereas ACh (3 μM) caused membrane hyperpolarization (−20.9±3.0 mV, n=25, P<0.05). The ACh‐induced membrane hypepolarization persisted after application of L‐NOARG (−23.5±5.9 mV, n=8, P<0.05) or glibenclamide (−20.6±5.4 mV, n=5, P<0.05) but was greatly diminished by apamin (reduced to −5.8±3.2 mV, n=3, P<0.05).
Sodium nitroprusside (0.1–10 μM) did not hyperpolarize the smooth muscle cell membrane potential (0.2±0.3 mV, n=4, P>0.05) but it greatly attenuated the His‐induced contraction in endothelium‐denuded strips (n=4, P<0.05).
These results suggest that, under the present experimental conditions: (i) spontaneous or basal release of NO from endothelial cells exerts a significant negative effect on agonist‐induced contractions in rabbit MCA, and (ii) ACh primarily activates the release of endothelium‐derived hyperpolarizing factor (EDHF) in rabbit MCA.
The characteristic features of the endothelium‐mediated regulation of the electrical and mechanical activity of the smooth muscle cells of cerebral arteries were studied by measuring membrane potential and isometric force in endothelium‐intact and ‐denuded strips taken from the rabbit middle cerebral artery (MCA).
In endothelium‐intact strips, histamine (His, 3–10 μM) and high K+ (20–80 mM) concentration‐dependently produced a transient contraction followed by a sustained contraction. Noradrenaline (10 μM), 5‐hydroxytryptamine (10 μM) and 9,11‐epithio‐11, 12‐methano‐thromboxane A2 (10 nM) each produced only a small contraction (less than 5% of the maximum K+‐induced contraction).
NG‐nitro‐L‐arginine (L‐NOARG, 100 μM), but not indomethacin (10 μM), greatly enhanced the phasic and the tonic contractions induced by His (1–10 μM) in endothelium‐intact, but not in endothelium‐denuded strips, suggesting that spontaneous or basal release of nitric oxide (NO) from endothelial cells potently attenuates the His‐induced contractions. Acetylcholine (ACh, 0.3–3 μM) caused concentration‐dependent relaxation (maximum relaxation by 89.7±7.5%, n=4, P<0.05) when applied to endothelium‐intact strips precontracted with His. L‐NOARG had little effect on this ACh‐induced relaxation (n=4; P<0.05). Apamin (0.1 μM), but not glibenclamide (3 μM), abolished the relaxation induced by ACh (0.3–3 μM) in L‐NOARG‐treated strips (n=4, P<0.05).
In endothelium‐intact tissues, His (3 μM) depolarized the smooth muscle membrane potential (by 4.4±1.8 mV, n=12, P<0.05) whereas ACh (3 μM) caused membrane hyperpolarization (−20.9±3.0 mV, n=25, P<0.05). The ACh‐induced membrane hypepolarization persisted after application of L‐NOARG (−23.5±5.9 mV, n=8, P<0.05) or glibenclamide (−20.6±5.4 mV, n=5, P<0.05) but was greatly diminished by apamin (reduced to −5.8±3.2 mV, n=3, P<0.05).
Sodium nitroprusside (0.1–10 μM) did not hyperpolarize the smooth muscle cell membrane potential (0.2±0.3 mV, n=4, P>0.05) but it greatly attenuated the His‐induced contraction in endothelium‐denuded strips (n=4, P<0.05).
These results suggest that, under the present experimental conditions: (i) spontaneous or basal release of NO from endothelial cells exerts a significant negative effect on agonist‐induced contractions in rabbit MCA, and (ii) ACh primarily activates the release of endothelium‐derived hyperpolarizing factor (EDHF) in rabbit MCA.
DOI: 10.1038/sj.bjp.0701285
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