In blood vessels vascular tone is controlled by sympathetic nervous activity, during which noradrenaline and ATP are released from perivascular nerves and contribute to sympathetically regulated vasoconstriction. In muscular arteries the contractile physiological responses to ATP are mediated through activation of P2X receptors, which are non-selective ligand-gated cation channels in the plasma membrane of vascular smooth muscle cells (VSMCs). Data about functional P2X receptors in human blood vessels are very limited; therefore the role of P2X receptors in VSMCs from human omental arteries (HOA) was studied in this work. This study conforms to the principles outlined in the Declaration of Helsinki and was approved by the local Research Ethics Committee (09/H0803/103) for retrieval of human tissue. Prior to surgery consent was obtained from patients undergoing elective abdominal surgery (n=7, 4 females, 3 females). Isolated VSMCs were obtained by enzymatic dispersion of small HOA blood vessels. The agonist-induced responses in [Ca2+]i were investigated in fluo-3 loaded HOA VSMCs using x-y laser scanning confocal imaging. The genes encoding P2X receptor subunits were identified in preparations obtained from manually collected isolated HOA VSMCs using RT-PCR analysis and the expression of corresponding proteins was confirmed by immunocytochemical and Western blot techniques. Application of 10 µmol/l ATP evoked a robust increase in [Ca2+]i in fluo-3 loaded VSMCs. 10 µmol/l of selective P2X receptor agonist α,βme-ATP evoked increase in [Ca2+]i with similar amplitude and kinetic of the fluorescent signal (101.7±4.8% of ATP response, n=7, p>0.05) suggesting that stimulatory action of ATP on [Ca2+]i is most likely mediated via activation of P2X receptors of the VSMC membrane. The exposure to 1 µmol/l selective P2X receptor antagonist NF279 significantly (by 32.3±5.5% of the control response, n=6, p<0.05) reduced the amplitude of [Ca2+]i increase evoked by 10 µmol/l α,βme-ATP. The RT-PCR analysis revealed that HOA VSMCs express genes for P2X1 and P2X4 receptor subunits. The expression of corresponding proteins was confirmed by fluorescent immunocytochemical visualisation of VSMCs labelled with antibody detecting P2X1 and P2X4 receptors. These experiments revealed the presence of P2X1 and P2X4 receptors subunit proteins in the plasma membrane but not in the deeper cytoplasm of VSMCs. The Western blot analysis of the fragments of the HOA showed the presence of monomeric and dimeric byproducts of P2X1 (60 and 120 kDA) and P2X4 (43 and 100 kDa) receptor subunits. These data suggest that VSMCs from HOA express P2X1 and P2X4 receptors subunits with homomeric P2X1 channel receptors serving as a predominant functional target for stimulatory action of extracellular ATP in these blood vessels.