Search

Adenosine is a purine nucleoside that regulates cell function through G protein-coupled receptors that activate or inhibit adenylyl cyclase. Based on the understanding that cAMP regulates alveolar epithelial active [Na.sup.+] transport, we hypothesized that adenosine and its receptors have the potential to regulate alveolar ion transport and airspace fluid content. Herein, we report that type 1 ([A.sub.1]R), 2a ([A.sub.2a]R), 2b ([A.sub.2b]R), and 3 ([A.sub.3]R) adenosine receptors are present in rat and mouse lungs and alveolar type 1 and 2 epithelial cells (AT1 and AT2). Rat AT2 cells generated and produced cAMP in response to adenosine, and micromolar concentrations of adenosine were measured in bronchoalveolar lavage fluid from mice. Ussing chamber studies of rat AT2 cells indicated that adenosine affects ion transport through engagement of [A.sub.1]R, [A.sub.2a]R, and/or [A.sub.3]R through a mechanism that increases CFTR and amiloride-sensitive channel function. Intratracheal instillation of low concentrations of adenosine ([less than or equal to] [10.sup.-8]M) or either [A.sub.2a]R- or [A.sub.3R]-specific agonists increased alveolar fluid clearance (AFC), whereas physiologic concentrations of adenosine ([greater than or equal to] [10.sup.-6]M) reduced AFC in mice and rats via an [A.sub.1]R-dependent pathway. Instillation of a CFTR inhibitor (CFT[R.sub.inh-172]) attenuated adenosine-mediated down-regulation of AFC, suggesting that adenosine causes C[I.sup.-] efflux by means of CFTR. These studies report a role for adenosine in regulation of alveolar ion transport and fluid clearance. These findings suggest that physiologic concentrations of adenosine allow the alveolar epithelium to counterbalance active [Na.sup.+] absorption with C[I.sup.-] efflux through engagement of the [A.sub.1]R and raise the possibility that adenosine receptor ligands can be used to treat pulmonary edema. active sodium transport | adenosine receptors | cystic fibrosis transmembrane conductance regulator

LPS is known to modulate macrophage responses during sepsis, including cytokine release, phagocytosis, and proliferation. Although agents that elevate cAMP reverse LPS-induced macrophage functions, whether LPS itself modulates cAMP and whether LPS-induced decreases in proliferation are modulated via a cAMP-dependent pathway are not known. Murine macrophages (RAW264.7 cells) were treated with LPS in the presence or absence of inhibitors of prostaglandin signaling, protein kinases, CaM, [G.sub.i] proteins, and NF-[kappa]B translocation or transcription/translation. LPS effects on CaMKII phosphorylation and the expression of relevant adenylyl cyclase (AC) isoforms were measured. LPS caused a significant dose (5-10,000 ng/ml)- and time (1-8 h)-dependent increase in forskolin-stimulated AC activity that was abrogated by pretreatment with SN50 (an NF-[Kappa]B inhibitor), actinomycin D, or cycloheximide, indicating that the effect is mediated via NF-[Kappa]B-dependent transcription and new protein synthesis. Furthermore, LPS decreased the phosphorylation state of CaMKII, and pretreatment with a CaM antagonist attenuated the LPS-induced sensitization of AC. LPS, cAMP, or PKA activation each independently decreased macrophage proliferation. However, inhibition of NF-[Kappa]B had no effect on LPS-induced decreased proliferation, indicating that LPS-induced decreased macrophage proliferation can proceed via PKA-independent signaling pathways. Taken together, these findings indicate that LPS induces sensitization of AC activity by augmenting the stimulatory effect of CaM and attenuating the inhibitory effect of CaMKII on isoforms of AC that are CaMK sensitive. cell culture; prostaglandin; phosphodiesterase; nuclear factor-[Kappa]B; calcium/calmodulin-dependent kinase; calmodulin

We have recently demonstrated protection against renal ischemic-reperfusion injury in vivo by [A.sub.1]- and [A.sub.2a]-adenosine receptor (AR) modulations. To further elucidate the signaling cascades of AR-induced cytoprotection against reperfusion/oxidant-mediated injury, immortalized human proximal tubule (HK-2) cells were treated with [H.sub.2][O.sub.2]. [H.sub.2][O.sub.2] caused dose- and time-dependent HK-2 cell death that was measured by lactate dehydrogenase release and trypan blue dye uptake. Adenosine protected against [H.sub.2][O.sub.2]-induced HK-2 cell death by means of [A.sub.1]- and [A.sub.2a]-AR activation. [A.sub.1]-AR-mediated protection involves pertussis toxin-sensitive G proteins and protein kinase C, whereas [A.sub.2a]-AR-mediated protection involves protein kinase A activation by means of cAMP and activation of the cAMP response element binding protein. Moreover, protein kinase A activators (forskolin and Sp-isomer cAMP) also protected HK-2 cells against [H.sub.2][O.sub.2] injury. De novo gene transcription and protein synthesis are required for both [A.sub.1]- and [A.sub.2a]-AR-mediated cytoprotection as actinomycin D and cycloheximide, respectively, blocked cytoprotection. Chronic treatments with a nonselective AR agonist abolished the protection by adenosine. Moreover, chronic treatments with a nonselective AR antagonist increased the endogenous tolerance of HK-2 cells against [H.sub.2][O.sub.2]. We concluded that [A.sub.1]- and [A.sub.2a]-AR activation protects HK-2 cells against [H.sub.2][O.sub.2]-induced injury by means of distinct signaling pathways that require new gene transcription and new protein synthesis. adenosine 3',5'-cyclic monophosphate; immortalized human proximal tubule cells; hydrogen peroxide; pertussis toxin-sensitive G proteins; protein kinase A; protein kinase C

A study was conducted on the 316L stainless steel powder that is subjected to single and double action die pressing to determine its densification behavior and the effect of friction between powders. Finite element method was used to calculate the density distribution of the powder during compression. Results have shown that different density distributions become similar when uniaxially compressed.