S70 two transmembrane domains, a large glycosylated extracel- lular domain, and intracellular N- and C-termini. Their functional subunit is a trimer, and they can form either a homomeric unit (with the exception of P2X6) or hetero- trimers with other P2X subunits which display properties that differ from the corresponding homomeric form. The P2X receptors play key roles in various physiological processes such as nerve transmission, pain sensation, and immune response [45], but open questions, with important physiological and pharmaceutical implications, still exist in this expanding field of research [46]. Alomone Labs invests great efforts in the development of antibodies that are tailored to the needs of the research community. Our antibody development process begins with a deep understanding of the structure, biology, and functionality of each and any one of the receptors and channels against which we prepare the antibodies. Our antibodies are prepared using a peptide chosen from the sequence of each one of the channels that is thoroughly examined to preclude cross- reactivity first of all with other members of the close channel family and then with other known non-related proteins. Our antibodies are always affinity purified in order to provide the best possible specific antibody content and avoid as much as possible unwanted non-relevant antibodies in the final antibody preparation. In addition, our antibodies are always rigorously tested in a Western blot assay in the appropriate target tissues to confirm functionality. Purinergic Signalling (2012) 8 (Suppl 1):S61–S79 Below, we have summarized for each P2X isoform recent literature citing the use of Alomone Labs anti-P2X receptor antibodies and the contribution of these works to our understanding of the roles played by P2X receptor channels in several physiological and pathophysiological processes. Due to space constrictions, only a handful of these contributions will be acknowledged, and we regret any inconvenience that this may arise. P2X1 P2X1 is relatively widely expressed with prominent expression in platelets, megakaryocytes, smooth muscles, and vas deferens. P2X1 is the sole P2X receptor present in platelets, and the activation of the receptor generates an increase in intracellular Ca2+, which in turn leads to the secretion of secretory granules and shape change [45, 47]. Indeed, using Alomone Labs anti-P2X1 receptor antibody (#APR-001), Vial et al. [48] showed the co-localization of P2X1 with CD41, a known marker of platelets and megakaryocytes, in samples obtained from bone marrow and spleen (Fig. 6, top panels). P2X1 platelet localization in human platelets was confirmed later by several groups using the anti-P2X1 receptor antibody [49, 50]. It is now widely recognized that P2X1 has a key role in platelet function. For instance, it has been shown that the Fig. 6 Co-localization of P2X1 and CD41 in bone marrow (top panel) and double immunofluorescence for P2X2R channel and orexin in hypothalamic neurons (bottom panel). Top panel, P2X1 receptor immunoreactivity (red, #APR-001) is co-localized with CD41 (green). Similar levels of immunoreactivity were detected in tissues from 5- day-old (left two images) and adult mice (right two images). Bottom panel, P2X2R channel staining (red, #APR-003) (a); orexin staining (green) (b); merge (c). Note that some P2X2R-labeled cells do not stain for orexin (arrows). f fornix. Top panels; adapted from reference 48 with permission of John Wiley and Sons (a–c). Adapted from reference 55 with permission of John Wiley and Sons