Effects of pH on Vascular Tone in Rabbit Basilar Arteries

Effects of pH on vascular tone and L-type Ca(2+) 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 (pH(o)) 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 pH(o) 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 pH(o), the effect of pH(o) on voltage-dependent L-type Ca(2+) channel (VDCC(L)) was studied. VDCC(L) was modulated by pH(o): the peak value of Ca(2+) channel current (I(Ba)) 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.