We investigated the role of hydrogen sulphide (H2S) in intracellular pH (pH(i)) regulation in vascular smooth muscle cells and its contribution on vasodilation. NaHS, a H2S donor, decreased pH(i) in a concentration-dependent manner ranging from 10 mu M to 1 mM. Neither inhibition of the Na+/H+ exchanger with 5-(N-ethyl-N-isopropyl) amiloride, (EIPA, 10 mu M), nor plasmalemnial Ca2+-ATPase with CdCl2 (20 nM) alters the effect of NaHS on pH(i). Blockade of the Cl-/HCO3-exchanger with 4,4 '-diisothiocyanatostilbene-2,2 '-disulfonic acid (DIDS) significantly attenuated the pHi lowering effect of NaHS. Moreover, NaHS significantly increased the activity of Cl-/HCO3-exchanger when measured with NH4Cl Prepulse method. DIDS attenuated the vasorelaxation induced by NaHS whereas EIPA and CdCl2 did not cause any change. In conclusion, H2S induced intracellular acidification via activation of Cl-/HCO3- exchanger, which is, at least partially, responsible for H2S-mediated vasorelaxation. (C) 2007 Elsevier Inc. All rights reserved.