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Effects of pH on vascular tone in rabbit basilar arteries.

Kim YC, Lee SJ, Kim KW - J. Korean Med. Sci. (2004)

Bottom Line: Since high K+- and histamine-induced tonic contractions were affected by nicardipine and pHo, the effect of pHo on voltage-dependent L-type Ca2+ channel (VDCCL) was studied.VDCCL was modulated by pHo: the peak value of Ca2+ channel current (IBa) at a holding of 0 mV decreased in [acidosis]o by 41+/-8.8%, whereas that increased in [alkalosis]o by 35+/-2.1% (n=3).These results suggested that the external pH regulates vascular tone partly via the modulation of VDCC in rabbit basilar arteries.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Chungbuk National University College of Medicine, Cheongju, Korea.

ABSTRACT
Effects of pH on vascular tone and L-type Ca2+ channels were investigated using Mulvany myograph and voltage-clamp technique in rabbit basilar arteries. In rabbit basilar arteries, high K+ produced tonic contractions by 11+/-0.6 mN (mean+/-S.E.,n=19). When extracellular pH (pHo) was changed from control 7.4 to 7.9 ([alkalosis]o), K+-induced contraction was increased to 128+/-2.1% of the control (n=13). However, K+-induced contraction was decreased to 73+/-1.3% of the control at pHo 6.8 ([acidosis] o, n=4). Histamine (10 microM) also produced tonic contraction by 11+/-0.6 mN (n=17), which was blocked by post-application of nicardipine (1 microM). [alkalosis]o and [acidosis]o increased or decreased histamine-induced contraction to 134+/-5.7% and 27+/-7.6% of the control (n=4, 6). Since high K+- and histamine-induced tonic contractions were affected by nicardipine and pHo, the effect of pHo on voltage-dependent L-type Ca2+ channel (VDCCL) was studied. VDCCL was modulated by pHo: the peak value of Ca2+ channel current (IBa) at a holding of 0 mV decreased in [acidosis]o by 41+/-8.8%, whereas that increased in [alkalosis]o by 35+/-2.1% (n=3). These results suggested that the external pH regulates vascular tone partly via the modulation of VDCC in rabbit basilar arteries.

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Effects of the repetitive alteration of pHo on high K+-induced contraction in rabbit basilar artery. Modulatory effects on high K+-induced contraction by the alteration of pHo was monitored by repetitive changes of pHo in rabbit basilar artery. (A) 50 mM of high K+-induced tonic contraction was repeatedly increased by pHo 7.9. (B) Acidotic and alkalotic conditions were induced to 50 mM of high K+-induced tonic contraction. Each condition of pHo 6.8 and 7.9 in a same tissue decreased and increased tonic contraction, respectively, in a reversible manner. (C) In the presence of L-NNA, enhancing effects of alkalotic condition on high K+-induced tonic contraction was studied by pre-application of pHo 7.9. Tonic contraction induced by application of 50 mM of high K+ solution (pHo 7.9) was decreased by post application of normal pH (pH 7.4).
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Figure 2: Effects of the repetitive alteration of pHo on high K+-induced contraction in rabbit basilar artery. Modulatory effects on high K+-induced contraction by the alteration of pHo was monitored by repetitive changes of pHo in rabbit basilar artery. (A) 50 mM of high K+-induced tonic contraction was repeatedly increased by pHo 7.9. (B) Acidotic and alkalotic conditions were induced to 50 mM of high K+-induced tonic contraction. Each condition of pHo 6.8 and 7.9 in a same tissue decreased and increased tonic contraction, respectively, in a reversible manner. (C) In the presence of L-NNA, enhancing effects of alkalotic condition on high K+-induced tonic contraction was studied by pre-application of pHo 7.9. Tonic contraction induced by application of 50 mM of high K+ solution (pHo 7.9) was decreased by post application of normal pH (pH 7.4).

Mentions: To exclude the effects of nitric oxide (NO) released from endothelial cells, nitro-L-arginine (L-NNA), an inhibitor of NO synthase, was used. In all experiments, 100 µM L-NNA was pretreated before the application of high K+ solution or the agonist. The pretreatment with L-NNA increased basal tone slightly by 1.1±0.2 mN (n=6, p>0.05, Fig. 1A). When high K+ solution was applied at the normal pHo, the arterial tone was greatly enhanced by 11.4±0.6 mN (n=19) and maintained at a sustained level (Fig. 1, 2). These tonic contractions was almost completely blocked by nicardipine (1 µM) to 7±3.9% (n=7) of the control (Fig. 5A). To elucidate the effects of pHo on K+-induced contraction, pHo was changed from 7.4 to 7.9 [alkalosis]o or to 6.8 [acidosis]o. When the pH of the bath solution was changed from 7.4 to 7.9, the high K+-induced contraction was enhanced reversibly to 128±2.1% (n=13, p<0.01, Fig. 1A, D). However, K+-induced contraction decreased to 87±1.0% and to 73±1.3% of the control at pHo 7.0 and 6.8 in a reversible manner, respectively (n=4, Fig. 1B-D). The effects of [alkalosis]o or [acidosis]o on the K+-induced contraction were also observed in the same tissue. As shown in Fig. 2A, B, enhancing and suppressing effects of pHo on high K+-induced tonic contractions were observed in the same tissue. The enhancing effects of [alkalosis]o on high K+-induced tonic contraction were also observed under the pre-application of pHo 7.9 (Fig. 2C).


Effects of pH on vascular tone in rabbit basilar arteries.

Kim YC, Lee SJ, Kim KW - J. Korean Med. Sci. (2004)

Effects of the repetitive alteration of pHo on high K+-induced contraction in rabbit basilar artery. Modulatory effects on high K+-induced contraction by the alteration of pHo was monitored by repetitive changes of pHo in rabbit basilar artery. (A) 50 mM of high K+-induced tonic contraction was repeatedly increased by pHo 7.9. (B) Acidotic and alkalotic conditions were induced to 50 mM of high K+-induced tonic contraction. Each condition of pHo 6.8 and 7.9 in a same tissue decreased and increased tonic contraction, respectively, in a reversible manner. (C) In the presence of L-NNA, enhancing effects of alkalotic condition on high K+-induced tonic contraction was studied by pre-application of pHo 7.9. Tonic contraction induced by application of 50 mM of high K+ solution (pHo 7.9) was decreased by post application of normal pH (pH 7.4).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 2: Effects of the repetitive alteration of pHo on high K+-induced contraction in rabbit basilar artery. Modulatory effects on high K+-induced contraction by the alteration of pHo was monitored by repetitive changes of pHo in rabbit basilar artery. (A) 50 mM of high K+-induced tonic contraction was repeatedly increased by pHo 7.9. (B) Acidotic and alkalotic conditions were induced to 50 mM of high K+-induced tonic contraction. Each condition of pHo 6.8 and 7.9 in a same tissue decreased and increased tonic contraction, respectively, in a reversible manner. (C) In the presence of L-NNA, enhancing effects of alkalotic condition on high K+-induced tonic contraction was studied by pre-application of pHo 7.9. Tonic contraction induced by application of 50 mM of high K+ solution (pHo 7.9) was decreased by post application of normal pH (pH 7.4).
Mentions: To exclude the effects of nitric oxide (NO) released from endothelial cells, nitro-L-arginine (L-NNA), an inhibitor of NO synthase, was used. In all experiments, 100 µM L-NNA was pretreated before the application of high K+ solution or the agonist. The pretreatment with L-NNA increased basal tone slightly by 1.1±0.2 mN (n=6, p>0.05, Fig. 1A). When high K+ solution was applied at the normal pHo, the arterial tone was greatly enhanced by 11.4±0.6 mN (n=19) and maintained at a sustained level (Fig. 1, 2). These tonic contractions was almost completely blocked by nicardipine (1 µM) to 7±3.9% (n=7) of the control (Fig. 5A). To elucidate the effects of pHo on K+-induced contraction, pHo was changed from 7.4 to 7.9 [alkalosis]o or to 6.8 [acidosis]o. When the pH of the bath solution was changed from 7.4 to 7.9, the high K+-induced contraction was enhanced reversibly to 128±2.1% (n=13, p<0.01, Fig. 1A, D). However, K+-induced contraction decreased to 87±1.0% and to 73±1.3% of the control at pHo 7.0 and 6.8 in a reversible manner, respectively (n=4, Fig. 1B-D). The effects of [alkalosis]o or [acidosis]o on the K+-induced contraction were also observed in the same tissue. As shown in Fig. 2A, B, enhancing and suppressing effects of pHo on high K+-induced tonic contractions were observed in the same tissue. The enhancing effects of [alkalosis]o on high K+-induced tonic contraction were also observed under the pre-application of pHo 7.9 (Fig. 2C).

Bottom Line: Since high K+- and histamine-induced tonic contractions were affected by nicardipine and pHo, the effect of pHo on voltage-dependent L-type Ca2+ channel (VDCCL) was studied.VDCCL was modulated by pHo: the peak value of Ca2+ channel current (IBa) at a holding of 0 mV decreased in [acidosis]o by 41+/-8.8%, whereas that increased in [alkalosis]o by 35+/-2.1% (n=3).These results suggested that the external pH regulates vascular tone partly via the modulation of VDCC in rabbit basilar arteries.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Chungbuk National University College of Medicine, Cheongju, Korea.

ABSTRACT
Effects of pH on vascular tone and L-type Ca2+ channels were investigated using Mulvany myograph and voltage-clamp technique in rabbit basilar arteries. In rabbit basilar arteries, high K+ produced tonic contractions by 11+/-0.6 mN (mean+/-S.E.,n=19). When extracellular pH (pHo) was changed from control 7.4 to 7.9 ([alkalosis]o), K+-induced contraction was increased to 128+/-2.1% of the control (n=13). However, K+-induced contraction was decreased to 73+/-1.3% of the control at pHo 6.8 ([acidosis] o, n=4). Histamine (10 microM) also produced tonic contraction by 11+/-0.6 mN (n=17), which was blocked by post-application of nicardipine (1 microM). [alkalosis]o and [acidosis]o increased or decreased histamine-induced contraction to 134+/-5.7% and 27+/-7.6% of the control (n=4, 6). Since high K+- and histamine-induced tonic contractions were affected by nicardipine and pHo, the effect of pHo on voltage-dependent L-type Ca2+ channel (VDCCL) was studied. VDCCL was modulated by pHo: the peak value of Ca2+ channel current (IBa) at a holding of 0 mV decreased in [acidosis]o by 41+/-8.8%, whereas that increased in [alkalosis]o by 35+/-2.1% (n=3). These results suggested that the external pH regulates vascular tone partly via the modulation of VDCC in rabbit basilar arteries.

Show MeSH
Related in: MedlinePlus