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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 alteration of the extracellular pH (pHo) on high K+-induced contraction in basilar arteries of rabbits. Mulvany myograph was used for recording isometric tension of rabbit basilar artery. All contractile experiments in this study were done in the presence of nitro-L-arginine (L-NNA, 100 µM). (A) Superfusion of 50 mM of high K+ solution to the bath provoked tonic contraction. This contraction was enhanced by pHo 7.9 in a reversible manner. (B, C) Under acidic condition such as pHo 7.0 or 6.8 tonic contraction was suppressed in a reversible manner. (D) Bar graphs show mean relative K+-induced contraction by alteration of pHo. Asterisks indicate the data which were considered to be significantly different from control data (**p<0.01).
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Figure 1: Effects of the alteration of the extracellular pH (pHo) on high K+-induced contraction in basilar arteries of rabbits. Mulvany myograph was used for recording isometric tension of rabbit basilar artery. All contractile experiments in this study were done in the presence of nitro-L-arginine (L-NNA, 100 µM). (A) Superfusion of 50 mM of high K+ solution to the bath provoked tonic contraction. This contraction was enhanced by pHo 7.9 in a reversible manner. (B, C) Under acidic condition such as pHo 7.0 or 6.8 tonic contraction was suppressed in a reversible manner. (D) Bar graphs show mean relative K+-induced contraction by alteration of pHo. Asterisks indicate the data which were considered to be significantly different from control data (**p<0.01).

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 alteration of the extracellular pH (pHo) on high K+-induced contraction in basilar arteries of rabbits. Mulvany myograph was used for recording isometric tension of rabbit basilar artery. All contractile experiments in this study were done in the presence of nitro-L-arginine (L-NNA, 100 µM). (A) Superfusion of 50 mM of high K+ solution to the bath provoked tonic contraction. This contraction was enhanced by pHo 7.9 in a reversible manner. (B, C) Under acidic condition such as pHo 7.0 or 6.8 tonic contraction was suppressed in a reversible manner. (D) Bar graphs show mean relative K+-induced contraction by alteration of pHo. Asterisks indicate the data which were considered to be significantly different from control data (**p<0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2822262&req=5

Figure 1: Effects of the alteration of the extracellular pH (pHo) on high K+-induced contraction in basilar arteries of rabbits. Mulvany myograph was used for recording isometric tension of rabbit basilar artery. All contractile experiments in this study were done in the presence of nitro-L-arginine (L-NNA, 100 µM). (A) Superfusion of 50 mM of high K+ solution to the bath provoked tonic contraction. This contraction was enhanced by pHo 7.9 in a reversible manner. (B, C) Under acidic condition such as pHo 7.0 or 6.8 tonic contraction was suppressed in a reversible manner. (D) Bar graphs show mean relative K+-induced contraction by alteration of pHo. Asterisks indicate the data which were considered to be significantly different from control data (**p<0.01).
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