Low Molecular Weight mRNA Encodes a Protein That Controls Serotonin 5-HT_(1c) and Acetylcholine M_1 Receptor Sensitivity in Xenopus Oocytes

Serotonin 5-HT_(1c) and acetylcholine M_1 receptors activate phosphoinositidase, resulting in an increased formation of IP_3 and 1,2 diacylglycerol. In Xenopus oocytes injected with mRNA encoding either of these receptors, Ca^(2+) released from intracellular stores in response to IP3 then opens Ca^(2+)-gated Cl^-channels. In the present experiments, oocytes expressing a transcript from a cloned mouse serotonin 5-HT_(1c) receptor were exposed to identical 15-s pulses of agonist, administered 2 min apart; the second current response was two to three times that of the first. However, in those oocytes coinjected with the 5-HT_(1c) receptor transcript and a low molecular weight fraction (0.3-1.5 kb) of rat brain mRNA, the second current response was ~50% of the first. Thus, the low molecular weight RNA encodes a protein (or proteins) that causes desensitization. Experiments using fura-2 or a Ca^(2+)-free superfusate indicated that desensitization of the 5-HT_(1c) receptor response does not result from a sustained elevation of intracellular Ca^(2+) level or require the entry of extracellular Ca^(2+). Photolysis of caged IP_3 demonstrated that an increase in IP_3 and a subsequent rise in Ca^(2+) do not produce desensitization of either the IP_3 or 5-HT_(1c) peak current responses. Furthermore, in oocytes coinjected with the low molecular weight RNA and a transcript from the rat M_1 acetylcholine receptor, the M_1 current response was greatly attenuated. Our data suggest that the proteins involved in attenuation of the M_1 current response and desensitization of the 5-HT_(1c) current response may be the same

PEG-Albumin Plasma Expansion Increases Expression of MCP-1 Evidencing Increased Circulatory Wall Shear Stress: An Experimental Study

Treatment of blood loss with plasma expanders lowers blood viscosity, increasing cardiac output. However, increased flow velocity by conventional plasma expanders does not compensate for decreased viscosity in maintaining vessel wall shear stress (WSS), decreasing endothelial nitric oxide (NO) production. A new type of plasma expander using polyethylene glycol conjugate albumin (PEG-Alb) causes supra-perfusion when used in extreme hemodilution and is effective in treating hemorrhagic shock, although it is minimally viscogenic. An acute 40% hemodilution/exchange-transfusion protocol was used to compare 4% PEG-Alb to Ringer’s lactate, Dextran 70 kDa and 6% Hetastarch (670 kDa) in unanesthetized CD-1 mice. Serum cytokine analysis showed that PEG-Alb elevates monocyte chemotactic protein-1 (MCP-1), a member of a small inducible gene family, as well as expression of MIP-1α, and MIP-2. MCP-1 is specific to increased WSS. Given the direct link between increased WSS and production of NO, the beneficial resuscitation effects due to PEG-Alb plasma expansion appear to be due to increased WSS through increased perfusion and blood flow rather than blood viscosity

The Different Function of Single Phosphorylation Sites of Drosophila melanogaster Lamin Dm and Lamin C

Lamins' functions are regulated by phosphorylation at specific sites but our understanding of the role of such modifications is practically limited to the function of cdc 2 (cdk1) kinase sites in depolymerization of the nuclear lamina during mitosis. In our study we used Drosophila lamin Dm (B-type) to examine the function of particular phosphorylation sites using pseudophosphorylated mutants mimicking single phosphorylation at experimentally confirmed in vivo phosphosites (S25E, S45E, T435E, S595E). We also analyzed lamin C (A-type) and its mutant S37E representing the N-terminal cdc2 (mitotic) site as well as lamin Dm R64H mutant as a control, non-polymerizing lamin. In the polymerization assay we could observe different effects of N-terminal cdc2 site pseudophosphorylation on A- and B-type lamins: lamin Dm S45E mutant was insoluble, in contrast to lamin C S37E. Lamin Dm T435E (C-terminal cdc2 site) and R64H were soluble in vitro. We also confirmed that none of the single phosphorylation site modifications affected the chromatin binding of lamin Dm, in contrast to the lamin C N-terminal cdc2 site. In vivo, all lamin Dm mutants were incorporated efficiently into the nuclear lamina in transfected Drosophila S2 and HeLa cells, although significant amounts of S45E and T435E were also located in cytoplasm. When farnesylation incompetent mutants were expressed in HeLa cells, lamin Dm T435E was cytoplasmic and showed higher mobility in FRAP assay