Effects of pH on vascular tone in rabbit basilar arteries.

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.