Uridine nucleotides are known to cause constriction of pulmonary arterial smooth muscle. However, the P2 receptor subtypes underlying the contractile effects of these nucleotides in the pulmonary circulation have not been determined. We have used myography and the patch-clamp recording technique to compare the effects of UTP and UDP in isolated small pulmonary arteries (diameter 100 to 400 microm) and their constituent smooth muscle cells. In endothelium-denuded arteries, both UTP and UDP (0.01 to 3 mmol/L) induced concentration-dependent increases in tension that were independent of P2X receptor stimulation. The UDP-mediated increase in tension was significantly less sensitive to the nonselective P2 receptor blocker suramin than the UTP-mediated increase in tension. In single isolated arterial myocytes, voltage-clamped at -50 mV (close to the resting membrane potential of these cells), application of both UTP and UDP evoked periodic oscillations of inward current primarily because of a Ca2+-activated Cl- current (ICl,Ca). Oscillations of ICl,Ca evoked by UTP were reversibly inhibited by suramin, although those evoked by UDP were insensitive to the antagonist. In addition to confirming the presence of classical P2Y2 receptors, these results also provide functional evidence for the existence of a novel UDP receptor in pulmonary arterial myocytes, which may contribute to pyrimidine-evoked vasoconstriction. This notion is supported by molecular evidence that demonstrates the presence of P2Y6 receptor transcripts in rat pulmonary arterial smooth muscle.

Neither the electrophysiological effects of purinergic receptor stimulation nor the role of ATP in regulating the tone of pulmonary arterial smooth muscle has been determined. Therefore, we investigated the effects of purine nucleotides on acutely dissociated smooth muscle cells from rat small pulmonary arteries using the patch-clamp recording technique. Extracellular application of ATP activated a fast transient inward current (which decayed in the continued presence of the nucleotide) and produced sustained periodic oscillations of predominantly inward current. Pharmacological and anion substitution experiments revealed that the transient inward current was carried by the movement of cations. In contrast, the periodic oscillations of current were due primarily to a Ca(2+)-activated Cl- current (ICl,Ca) dependent on the release of Ca2+ from intracellular stores. Experiments using ATP analogues revealed the following order of potency for activation of the fast transient inward current: 2-methylthio ATP (2-meSATP) > ATP > alpha,beta-methylene ATP (alpha,beta-meATP) > > ADP > UTP = adenosine. Cross desensitization was seen between applications of ATP, alpha,beta-meATP, and 2-meSATP, suggesting that these agonists act via a common site. The order of potency for activation of ICl,Ca was UTP = ATP > > ADP > or = 2-meSATP > alpha,beta-meATP = adenosine. Both the fast transient inward current and ICl,Ca evoked by ATP and its analogues were abolished by the nonselective P2 purinoceptor antagonist suramin. These results show the existence of P2x and P2U purinoceptor subtypes in pulmonary arterial smooth muscle cells. Stimulation of these receptors results in activation of a fast transient inward cation current and ICl,Ca, respectively. It is likely that ATP acts via these receptor subtypes to regulate pulmonary arterial tone under physiological or pathological conditions.

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Objectives: We investigated effects of monoacylglyceride (MG) and free fatty acids (end products of fat hydrolysis in the gut) inclusion in infant formula’s fat‐blend on calcium and fat absorption. Methods: A randomized, blinded, 4 wk crossover study evaluated calcium and fat absorption and gastrointestinal tolerance in 2‐4 mo old healthy term infants fed an experimental milk‐based powdered formula containing MG palmitate and soy calcium fatty acids (EF) vs a similar commercial control formula containing triacylglyceride‐based fat‐blend (CF). Balance and tolerance data was based on 12 and 13 evaluable subjects, respectively. Results: Balance data indicated that percent (%) calcium absorption (primary study variable) was not different (p=0.85) between EF (38+5; mean±SEM) and CF (37+6). Absorbed calcium (mg/kg/day) was numerically higher (16%) with EF, but not statistically different. Percent fat absorption was 5.2% lower (p=0.01) with EF vs CF, but absorbed fat (g/kg/day) was numerically greater (9.4%) with EF. Tolerance data indicated that mean rank stool consistency was firmer (p=0.02) and stool frequency was higher (p=0.01) with EF vs CF. Percentage of yellow stools was higher (p=0.03) and percentage of green stools (p=0.03) was lower with EF vs CF. Mean rank fussiness was lower (p= 0.01) with EF vs CF. Conclusion: The EF demonstrated similar calcium absorption and good GI tolerance vs the CF, which was a standard formula containing a fat blend with proven efficacy and safe use in normal infants. Grant Funding Source: Supported by Abbott Nutrition