Effects of pH on Vascular Tone in Rabbit Basilar Arteries

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 rabbitbasilar 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 µM) also produced tonic contraction by 11±0.6 mN (n=17), which was blocked by post-application of nicardipine (1 µM). [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.

pCO2 and pH regulation of cerebral blood flow

“…Possibly consistent with these findings (Zuccarello et al, 2000a,b,c) are observations in rabbit basilar and cat middle cerebral artery ring/strip preparations in which elevation of extracellular pH did not cause or elicited only minimal contraction (Edvinsson and Sercombe, 1976; Aoyama et al, 1999; Kim et al, 2004). Additionally, contraction of cat middle cerebral artery rings to pH 7.4/pCO 2 14 mmHg solution was highly variable and, in some cases, minimal (Harder and Madden, 1985).…”

“…In other vascular preparations, elevated pH appears insufficient to elicit contraction (Edvinsson and Sercombe, 1976 ; Aoyama et al, 1999 ; Kim et al, 2004 ). Specifically, in rabbit basilar artery ring/strip preparations elevation of extracellular pH to 7.9 with unchanged CO 2 did not cause contraction (Aoyama et al, 1999 ; Kim et al, 2004 ).…”

“…In other vascular preparations, elevated pH appears insufficient to elicit contraction (Edvinsson and Sercombe, 1976 ; Aoyama et al, 1999 ; Kim et al, 2004 ). Specifically, in rabbit basilar artery ring/strip preparations elevation of extracellular pH to 7.9 with unchanged CO 2 did not cause contraction (Aoyama et al, 1999 ; Kim et al, 2004 ). Whether the lack of contraction in response to elevated pH was the result of nitric oxide synthase (NOS) inhibition by N ω -nitro-L-arginine (L-NNA; Kim et al, 2004 ) or absence of the endothelium (Aoyama et al, 1999 ) should be considered.…”

“…Specifically, in rabbit basilar artery ring/strip preparations elevation of extracellular pH to 7.9 with unchanged CO 2 did not cause contraction (Aoyama et al, 1999 ; Kim et al, 2004 ). Whether the lack of contraction in response to elevated pH was the result of nitric oxide synthase (NOS) inhibition by N ω -nitro-L-arginine (L-NNA; Kim et al, 2004 ) or absence of the endothelium (Aoyama et al, 1999 ) should be considered. On the other hand, in cat middle cerebral artery rings presumably with intact endothelium, elevation of extracellular pH only occasionally induced contraction and, even then, the contraction was of small magnitude (Edvinsson and Sercombe, 1976 ).…”

Brain lactate synthesis in thiamine deficiency: A re‐evaluation using 1H‐13C nuclear magnetic resonance spectroscopy

“…In support of this possibility, a previous report described reductions in pH consistent with focal lactic acidosis in vulnerable brain regions in pyrithiamine‐induced TD (Hakim, 1984). Altered pH is known to adversely affect vascular tone (Kim et al, 2004) and calcium homeostasis (Hriciga and Lehn, 1983). Whether glucose loading causes more intense acidosis in vulnerable brain structures in TD requires further study.…”