Stimulation of 32Pi transport into human erythrocyte ghosts and reconstituted vesicles by Mg2+ and hemoglobin

Human erythrocyte ghosts catalyze a low rate of 32Pi uptake. A severalfold stimulation of 32Pi uptake was observed after exposure of the membranes to an erythrocyte lysate or to hemoglobin in the presence of Mg2+. Ghosts prepared from erythrocytes that had been exposed to 10 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid showed a marked reduction in 32Pi uptake. Reconstitution of membranes with added phospholipids by freezing and thawing, by octylglucoside dilution or by cholate dialysis, yielded vesicles that catalyzed 32Pi uptake. When membranes were incubated with hemoglobin and Mg2+ prior to reconstitution, the rate of uptake was increased severalfold. The inhibition of hemoglobin and Mg2+-dependent uptake of 32Pi by chloride suggests that the transport in the reconstituted vesicles is catalyzed by the classical inorganic anion transporter.     

A rapid method for cloning and sequencing variable-region genes of expressed immunoglobulins

A rapid procedure is described for cloning immunoglobulin V region genes from cells that express them. cDNA is synthesized from mRNA template using primers homologous to the immunoglobulin constant-region genes. Blunt-ended, double-stranded cDNA is obtained by sequential addition of enzymes to a single tube. The cDNA is inserted directly into the M13 vector, which is screened by plaque lifting for the presence of specific inserts. Screening probes can be generated from 32P-labeled single-stranded cDNAs generated from primers different from those used for cloning, or alternatively, from previously cloned V or C gene segments. The ease of cloning a cDNA V region is directly related to the abundance of Ig-specific mRNA within the cell of interest. This method minimizes the number of steps and the time needed to obtain accurate and complete sequences of any expressed Ig V region gene.     

CGS8216 noncompetitively antagonizes the discriminative effects of diazepam in rats

The benzodiazepine antagonist properties of CGS8216 were evaluated in rats trained to discriminate between saline and 1.0 mg/kg of diazepam in a two-choice, stimulus-shock termination procedure. CGS8216 (0.3 to 100 mg/kg) administered alone, either s.c., p.o. or i.p., occasioned only saline-appropriate responding. When administered concomitantly with a constant 1.0 mg/kg dose of diazepam, CGS8216 produced dose-related decreases in drug-appropriate responding. CGS8216 was most potent by the i.p. route, and approximately tenfold less potent by the oral route. CGS8216 was dermatotoxic after s.c. administration. CGS8216 i.p. had a long duration of action. A dose of 30 mg/kg completely antagonized the discriminative effects of the 1.0 mg/kg training dose of diazepam when the antagonist was administered 8 hr before the start of the test session. In order to determine the type of antagonism by CGS8216, the dose-effect curve for diazepam was redetermined in the presence of varying doses of CGS8216 (0.3 to 3.0 mg/kg, i.p.). CGS8216 produced a dose-related rightward shift in the diazepam dose-effect curve, but also decreased the slope and appeared to decrease the maximal effect. These results are consistent with the interpretation that CGS8216 antagonizes diazepam in a noncompetitive manner. It may do so because either it interacts with a subpopulation of benzodiazepine receptors, it functions as a pseudo-irreversible antagonist due to its high affinity, or because it is an antagonist with agonist properties.     

Adenosine mediates transforming growth factor-beta 1 release in kidney glomeruli of diabetic rats

Up regulation of the transforming growth factor-beta 1 (TGF-β1) axis has been recognized as a pathogenic event for progression of glomerulosclerosis in diabetic nephropathy. We demonstrate that glomeruli isolated from diabetic rats accumulate up to sixfold more extracellular adenosine than normal rats. Both decreased nucleoside uptake activity by the equilibrative nucleoside transporter 1 and increased AMP hydrolysis contribute to raise extracellular adenosine. Ex vivo assays indicate that activation of the low affinity adenosine A_2B receptor subtype (A_2BAR) mediates TGF-β1 release from glomeruli of diabetic rats, a pathogenic event that could support progression of glomerulopathy when the bioavailability of adenosine is increased.     

The N terminus of the cardiac L-type Ca(2+) channel alpha(1C) subunit. The initial segment is ubiquitous and crucial for protein kinase C modulation, but is not directly phosphorylated.

The first 46 amino acids (aa) of the N terminus of the rabbit heart (RH) L-type cardiac Ca(2+) channel alpha(1C) subunit are crucial for the stimulating action of protein kinase C (PKC) and also hinder channel gating (Shistik, E., Ivanina, T., Blumenstein, Y., and Dascal, N. (1998) J. Biol. Chem. 273, 17901-17909). The mechanism of PKC action and the location of the PKC target site are not known. Moreover, uncertainties in the genomic sequence of the N-terminal region of alpha(1C) leave open the question of the presence of RH-type N terminus in L-type channels in mammalian tissues. Here, we demonstrate the presence of alpha(1C) protein containing an RH-type initial N-terminal segment in rat heart and brain by using a newly prepared polyclonal antibody. Using deletion mutants of alpha(1C) expressed in Xenopus oocytes, we further narrowed down the part of the N terminus crucial for both inhibitory gating and for PKC effect to the first 20 amino acid residues, and we identify the first 5 aa as an important determinant of PKC action and of N-terminal effect on gating. The absence of serines and threonines in the first 5 aa and the absence of phosphorylation by PKC of a glutathione S-transferase-fusion protein containing the initial segment suggest that the effect of PKC does not arise through a direct phosphorylation of this segment. We propose that PKC acts by attenuating the inhibitory action of the N terminus via phosphorylation of a remote site, in the channel or in an auxiliary protein, that interacts with the initial segment of the N terminus.