Under voltage‐clamp conditions, the activity of agonists and antagonists at a recombinant P2X₂ receptor expressed in Xenopus oocytes was examined at different levels of extracellular pH (pH_e). In normal Ringer (Mg²⁺ ions absent), the amplitude of submaximal inward currents to ATP was increased by progressively lowering pH_e (8.0–5.5). ATP‐responses reached a maximum at pH 6.5 with a 5 fold increase in ATP‐affinity; the apparent pK_a was 7.05±0.05. Receptor affinity for ATP was lowered when extracellular Ca²⁺ ions were replaced with equimolar Mg²⁺ ions. However, the amplitude of the ATP‐responses was still enhanced under acidic conditions, reaching maximal activity at pH 6.5 with a 5 fold increase in ATP‐affinity; the apparent pK_a was 7.35±0.05. ATP species present in the superfusate (for the above ionic conditions and pH levels) were calculated to determine the forms of ATP which activate P2X₂ receptors: possible candidates include HATP, CaHATP and MgHATP. However, levels of these protonated species increase below pH 6.5, suggesting that receptor protonation rather than agonist protonation is more important. The potency order for agonists of P2X₂ receptors was: ATP>2‐MeS‐ATPATPγS> ATPαS>>CTPBzATP, while other nucleotides were inactive. EC₅₀ and n_H values for full agonists were determined at pH 7.4 and re‐examined at pH 6.5. Extracellular acidification increased the affinity by approximately 5 fold for full agonists (ATP, 2‐MeSATP, ATPγS and ATPαS), without altering the potency order. The potency order for antagonists at P2X₂ receptors was: Reactive blue‐2>trinitrophenol‐ATPPalatine fast blackCoomassie brilliant bluePPADS>suramin (at pH 7.4). IC₅₀ values and slopes of the inhibition curves were re‐examined at different pH levels. Only blockade by suramin was affected significantly by extracellular acidification (IC₅₀ values: 10.4±2 μM, at pH 7.4; 78±5 nM, at pH 6.5; 30±6 nM, at pH 5.5). In summary, a lowered pH_e enhanced the activity of all agonists at P2X₂ receptors but, with the exception of suramin, not antagonists. Since a lowered pH_e is also known to enhance agonist activity at P_2X receptors on sensory neurones containing P2X₂ transcripts, the sensitization by metabolic acidosis of native P_2X receptors containing P2X₂ subunits may have a significant effect on purinergic cell‐to‐cell signalling.

A full pharmacological characterization was carried out on a recombinant ATP-gated ion channel (P_2times2 purinoceptor) expressed in Xenopus oocytes. This slowly-desensitizing neuronal P_2times2 purinoceptor, activated by ATP (EC₅₀ = 4.6 ± 1 μm at pH 7.4; n 4), showed the agonist potency order: ATP ≥ 2- MeSATP = ATPγS ≥ ATPαS < < Bz-ATP. The receptor affinity for ATP was enhanced 5–10 fold by acidifying the bathing solution (to pH 6.5) but was diminished 4–5 fold in an alkaline solution (pH 8.0). The maximum activity of P_2times2 purinoceptors and the activity order of a series of nucleotides were unaltered by changing extracellular pH. Interestingly, ATP sensitivity at a recombinant P_2Y1, purinoceptor remained unaltered with changing extracellular pH. These results indicate that acidotic conditions in the synaptic cleft could strengthen purinergic transmission at neuronal P_2times2 purinoceptors.

We aimed to map the resource use during systematic review (SR) production and reasons why steps of the SR production are resource intensive to discover where the largest gain in improving efficiency might be possible. We conducted a scoping review. An information specialist searched multiple databases (e.g., Ovid MEDLINE, Scopus) and implemented citation-based and grey literature searching. We employed dual and independent screenings of records at the title/abstract and full-text levels and data extraction. We included 34 studies. Thirty-two reported on the resource use-mostly time; four described reasons why steps of the review process are resource intensive. Study selection, data extraction, and critical appraisal seem to be very resource intensive, while protocol development, literature search, or study retrieval take less time. Project management and administration required a large proportion of SR production time. Lack of experience, domain knowledge, use of collaborative and SR-tailored software, and good communication and management can be reasons why SR steps are resource intensive. Resource use during SR production varies widely. Areas with the largest resource use are administration and project management, study selection, data extraction, and critical appraisal of studies.