The effects of ouabain and potassium on peritoneal fluid and solute transport characteristics

BACKGROUND

We reported anomalous transport characteristics of potassium during experimental peritoneal dialysis in rats and suggested that mechanisms of peritoneal potassium transport could be other than simple passive transport. Intracellular transport of potassium in cultured human mesothelial cells was reported to be regulated by three different pathways, such as channels blocked by ouabain, channels blocked by furosemide, and other.

OBJECTIVE

To investigate the effect of ouabain on peritoneal potassium and water transport characteristics.

METHODS

A single 4-hour peritoneal dwell was performed in 28 Sprague-Dawley rats. To minimize the diffusive transport of potassium, 4.5 mmol/L of KCl was added into conventional dialysis solution with 3.86% glucose [acidic peritoneal dialysis solution (APD)]. To evaluate the effect of the pH of dialysis solution on the transport of potassium and water, 4 mmol/L of NaOH was added into the potassium-containing study solutions [neutral peritoneal dialysis solution (NPD)]. To evaluate the effect of a potassium channel blocker on peritoneal potassium transport ATPase sensitive Na+-K+-transport inhibitor, ouabain (10(-5) mmol/L) was added to dialysis solutions immediately before the dwell study in eight rats with APD (APD-O) and six rats with NPD (NPD-O). Ouabain was not added in eight and six rats with APD and NPD (APD-C and NPD-C, respectively). They were used as control. Infusion volume was 30 mL. The intraperitoneal volume (V(D)) was estimated by using a volume marker dilution method with corrections for the elimination of volume marker, radioiodinated human serum albumin (RISA), from the peritoneal cavity (K(E)). The diffusive mass transport coefficient (K(BD)) and sieving coefficient (S) were estimated using the modified Babb-Randerson-Farrell model.

RESULTS

V(D) was significantly higher (p < 0.05 from 90 min to 240 min) and K(E) (0.027+/-0.018 mL/min for APD-O, 0.026+/-0.017 mL/min for NPD-O, and 0.030+/-0.022 mL/min for NPD-C, vs 0.058+/-0.030 mL/min for APD-C, p < 0.05 for each) significantly lower during dialysis with APD-O, NPD-O, and NPD-C than with APD-C. The intraperitoneal glucose expressed as a percentage of the initial amount was significantly higher with APD-O, NPD-C, and NPD-O than with APD-C (p < 0.05 from 90 min to 240 min). K(BD) for sodium was higher during dialysis with ouabain than without ouabain, while K(BD) for urea, glucose, and potassium, and S for urea, glucose, sodium, and potassium did not differ between the four groups.

CONCLUSIONS

The physiologic potassium concentration in neutral dialysis solutions and the use of ouabain decreased the intraperitoneal fluid absorption. The diffusive transport coefficient and sieving coefficient for potassium did not differ, while the diffusive transport coefficient for sodium increased during use of ouabain.

Novel mutations in the polyadenine tract of the transforming growth factor beta type II receptor gene are found in a subpopulation of human pancreatic adenocarcinomas

In this study, we determined the incidence of microsatellite instability (MIN) in pancreatic adenocarcinoma and determined whether MIN might target, for mutations, the simple nucleotide repeats of the transforming growth factor beta type II receptor (TGFBR2) gene. Forty-eight surgically resected pancreatic tumor tissue samples and two normal pancreas tissue samples were analyzed in this study. Microsatellite analysis was performed for six loci in 14 of the 48 tumor specimens for which we had matching normal genomic DNA. Only four of the 14 tumors (29%) were MIN-positive as determined by the presence of microsatellite variations in more than one locus. Interestingly, eight of the 14 specimens (57%) showed microsatellite variations or loss of heterozygosity at D18S34, suggesting that this locus may be a critical region of genetic instability in pancreatic tumorigenesis. Of the 48 tumors, only two (4%) showed mutations in the polyA region, one of the MIN-targeted sites of the TGFBR2 gene. DNA sequence analysis of these two specimens showed the presence of a two-base deletion in one tumor specimen and the other tumor specimen showed a base substitution in the polyA tract at codon 128 of the TGFBR2 gene. The fact that these mutations occurred in the polyA tract of some pancreatic tumors suggests that a subpopulation of these tumors may be susceptible to MIN-targeted mutations. The incidence of these mutations are low and similar to that reported for nonhereditary, sporadic colon cancers.

Coupled transcriptional and translational control of cyclin-dependent kinase inhibitor p18INK4c expression during myogenesis

Terminal differentiation of many cell types involves permanent withdrawal from the cell division cycle. The p18INK4c protein, a member of the p16/INK4 cyclin-dependent kinase (CDK) inhibitor family, is induced more than 50-fold during myogenic differentiation of mouse C2C12 myoblasts to become the predominant CDK inhibitor complexed with CDK4 and CDK6 in terminally differentiated myotubes. We have found that the p18INK4c gene expresses two mRNA transcripts--a 2.4-kb transcript, p18(L), and a 1.2-kb transcript, p18(S). In proliferating C2C12 myoblasts, only the larger p18(L) transcript is expressed from an upstream promoter. As C2C12 cells are induced to differentiate into permanently arrested myotubes, the abundance of the p18(L) transcript decreases. The smaller p18(S) transcript expressed from a downstream promoter becomes detectable by 12 h postinduction and is the predominant transcript expressed in terminally differentiated myotubes. Both transcripts contain coding exons 2 and 3, but p18(L) uniquely contains an additional noncoding 1.2-kb exon, exon 1, corresponding exclusively to the 5' untranslated region (5' UTR). The expression pattern of the shorter p18(S) transcript, but not that of the longer p18(L) transcript, correlates with terminal differentiation of muscle, lung, liver, thymus, and eye lens cells during mouse embryo development. The presence of the long 5' UTR in exon 1 attenuated the translation of p18(L) transcript, while its absence from the shorter p18(S) transcript resulted in significantly more efficient translation of the p18 protein. Our results demonstrate that during terminal muscle cell differentiation, induction of the p18 protein is regulated by promoter switching coupled with translational control.

Postnatal development of somatostatin- and neuropeptide Y-immunoreactive neurons in rat cerebral cortex: a double-labeling immunohistochemical study

The postnatal development of somatostatin (SOM)- and neuropeptide Y (NPY)-immunoreactive (ir) neurons was examined in rat cerebral cortex, while considering their coexistence in cortical neurons. Using double immunohistochemical staining for SOM and NPY with diaminobenzidine and benzidine dihydrochloride as chromogens, we subdivided immunoreactive cells into double-labeled SOM/NPY-, SOM only-, and NPY only-ir neurons. SOM/NPY- and SOM only-ir neurons were detectable even at the day of birth, in contrast on NPY only-ir cells which first appeared in most cortices from week two. The morphological features of double-labeled SOM/NPY neurons differed with those of SOM only- and NPY only-ir neurons. No apparent changes in the shape and size of single-labeled neurons occurred with age; throughout their postnatal life they were round and ovoid, had a thin rim of perinuclear cytoplasm, and short processes. However, the features of SOM/NPY-ir neurons were not consistent according to postnatal age; by day P7, these neurons showed immature features and they began to show more advanced neuronal characteristics by week P2, when they had a larger and more intensely-stain cytoplasm. In addition, their processes were longer, thicker and more complex than at earlier ages. At this age, SOM/NPY-ir somata were close to their near maximum size. From week P4, they became smaller and were lightly labeled. SOM/NPY-ir somata were larger than SOM only- and NYP only-ir somata at and after two weeks of age. The present results, showing different postnatal maturation patterns such as time of appearance and morphological features, raise the possibilities that double-labeled SOM/NPY and single-labeled immunoreactive neurons may be different populations regulated by different mechanisms in their development, and with different functional properties during development.

A protein phosphatase-1-binding motif identified by the panning of a random peptide display library

An unusually large number of regulatory or targeting proteins that bind to the catalytic subunit of protein phosphatase-1 have been recently reported. This can be explained by their possession of a common protein motif that interacts with a binding site on protein phosphatase-1. The existence of such a motif was established by the panning of a random peptide library in which peptide sequences are displayed on the Escherichia coli bacterial flagellin protein for bacteria that bound to protein phosphatase-1. There were 79 isolates containing 46 unique sequences with the conserved motif VXF or VXW, where X was most frequently His or Arg. In addition, this sequence was commonly preceded by 2-5 basic residues and followed by 1 acidic residue. This study demonstrates that binding to protein phosphatase-1 can be conferred to a protein by the presentation of a peptide motif on a surface loop. This binding motif is found in a number of protein phosphatase-1-binding proteins.

Retinoblastoma gene deficiency has mitogenic but not tumorigenic effects on erythropoiesis

The retinoblastoma protein (Rb), an important ubiquitous cell cycle regulator, was initially identified as the retinoblastoma tumor suppressor. To further address the activities of Rb in proliferation and tumorigenesis in the hematopoietic lineage, we transplanted Rb-/- fetal liver cells into sibling mice and assessed the outcome of Rb-/- hematopoietic cells in both short-term and long-term studies. Rb-/- hematopoietic cells rescued lethally irradiated mice with an efficiency comparable to that of wild-type cells. In spleen colony-forming unit assays, proliferation rates of the Rb-/- cells were greater than those of the wild-type cells. Similarly, in vitro burst-forming unit-erythroid and colony-forming unit-erythroid assays showed increased erythroid colony numbers from Rb-/- embryonic livers. Recipients of Rb-/- cells lived for more than 15-18 months, and most blood cell lineages matured normally with the expected switch from fetal to adult hemoglobin. However, the continued presence of nucleated erythrocytes in the peripheral blood and extensive extramedullary erythropoiesis indicated that the Rb-/- erythrocytes were not completely normal. No erythroleukemia developed during the 15-18 month period following transplantation. These results demonstrate the mitogenic effect but not tumorigenic transformation in erythrocyte lineage in the absence of Rb, which is distinct from the effect of Rb deficiency in neuroectodermal cells. The study supports the prevalent model that loss of the ubiquitously expressed tumor suppressor gene predisposes to only a limited spectrum of tumors.

Choline deficiency augments and antibody to tumor necrosis factor-alpha attenuates endotoxin-induced hepatic injury

Alcoholic liver disease can be associated with hepatic choline deficiency and hepatic steatosis, abnormalities also observed in rats administered choline-deficient (CD) diets. Bacterial lipopolysaccharides (LPS) have been postulated to play a key role in this choline deficiency model of liver injury, and LPS hepatotoxicity is mediated to a major extent by the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). This study addressed the following questions: Does LPS administration exacerbate an in vivo liver injury induced by choline deficiency? If so, do CD rats have increased serum TNF-alpha concentrations and does pretreatment anti-TNF-alpha IgG attenuate this injury? Rats administered choline-sufficient (CS) or CD diets for 16 days were intravenously administered either saline or LPS. One group of CD rats also received a single dose of anti-TNF-alpha IgG before LPS administration. Changes in histology and serum transaminase levels were determined. Both liver histology and serum transaminases were unchanged in the CS group treated with LPS, compared with the CS group treated with saline (control group). However, compared with this control group, transaminases were 5- to 7-fold higher in saline-treated CD rats and 30- to 50-fold higher in LPS-treated CD rats. Livers of saline-treated CD rats had massive fatty infiltration, and no necrosis but livers of LPS-treated CD rats showed both extensive fatty infiltration and large areas of necrosis. Serum TNF-alpha concentrations in CD rats (saline or LPS treated) were significantly elevated, compared with levels in corresponding CS rats. Pretreatment with the anti-TNF-alpha IgG prevented hepatonecrosis in LPS-treated CD rats and lowered their serum transaminases by one-third. Thus, LPS administration exacerbated liver injury induced by choline deficiency, and this injury was probably partially mediated by TNF-alpha and attenuated by anti-TNF-alpha IgG.

[The retinoblastoma gene: from its basic understanding as a signal mediator for growth and differentiation to its use in the treatment of cancer]

The retinoblastoma gene (RB) plays important roles in the genesis of human cancers. Several pieces of evidence have shown that the retinoblastoma protein (Rb) has dual roles in gating cell cycle progression and promoting cellular differentiation. The molecular mechanisms involved in these roles have been elucidated in some biological systems: Rb sequesters the transcription factors of E2F-1 to regulate entry of cell cycle, but enhances the activities of transcription factors such as C/ EBPs to initiate terminal differentiation. Thus, the Rb protein can serve as a mediator of extracellular signals for growth or differentiation. RB also has a tumor suppression function. Introduction of wild-type RB into human tumor cells deficient for RB suppresses their tumorigenicity in nude mice. Similarly, mice with RB+/- genotypes created by gene knockout methods spontaneously develop melanotrophic tumors with complete penetrance. Immune-competent RB+/- mice benefited significantly from adenovirus-mediated RB gene therapy. The fundamental knowledge of Rb function will allow us to take the next steps toward the use of tumor suppressor genes in the treatment of human cancer.

Colorimetric protein phosphatase inhibition assay of laboratory strains and natural blooms of cyanobacteria: comparisons with high-performance liquid chromatographic analysis for microcystins

Microcystins are cyclic heptapeptide hepatotoxins commonly produced by bloom-forming genera of cyanobacteria. These toxins are potent and specific inhibitors of protein phosphatases 1 and 2A. We have optimised a rapid, simple and sensitive colorimetric protein phosphatase 1 inhibition assay, utilising the activity of protein phosphatase 1 as expressed in a recombinant strain of Escherichia coli, towards the chromogenic substrate, p-nitrophenyl phosphate. A standard curve for the inhibition of protein phosphatase 1 by microcystin-LR was constructed with an IC50 of about 38 ng ml-1 and a limit of detection of 10-20 ng ml-1. Twenty-three laboratory-grown strains and 25 natural bloom samples of cyanobacteria were analysed by high-performance liquid chromatography for microcystins and by the protein phosphatase 1 inhibition assay. Agreement for the microcystin contents of the samples detected by high-performance liquid chromatography and the protein phosphatase 1 inhibition assay showed good correlation (R2 > 0.93, P < 0.0001). The suitability of the colorimetric protein phosphatase 1 inhibition assay as a screen for cyanobacterial microcystins is discussed.

Prolonged bleeding time: a new clinical manifestation of hepatocellular carcinoma?

The association between prolonged bleeding time and hepatocellular carcinoma (HCC) has not been well studied. We investigated whether bleeding time is prolonged in cirrhotic patients with HCC and studied the role of clinical characteristics, tumour size, and laboratory data in predicting bleeding time prolongation. After excluding patients that presented with blood dyscrasia and uraemia, 58 cirrhotic patients with HCC, 106 cirrhotic patients without HCC, and 44 age-and sex-matched healthy subjects were included in the study. Bleeding time, imaging studies, clinical characteristics and biochemical data were obtained for every patient. Cirrhotic patients with and without HCC had longer bleeding times (554 +/- 32 s, respectively) compared with healthy controls (357 +/- 13 s, P < 0.05). Hepatocellular carcinoma patients with a large tumour burden (> 5 cm in diameter) had a significantly longer bleeding time than those patients without (663 +/- 105 vs 376 +/- 23 s, respectively, P < 0.05). After excluding patients with a platelet count < or = 80 000/mm3, cirrhotic patients classified as Child-Pugh's grading A and with a large tumour burden had longer bleeding times(580 +/- 87 s) than patients with a small tumour burden (< or = 5cm in diameter) and cirrhotic patients without HCC (371 +/- 22 and 416 +/- 29 s, respectively, P < 0.05). In cirrhotic patients with HCC, higher serum bilirubin levels, a Child-Pugh's grading C, and a tumour size > 5 cm in diameter were found to be significant predictors for prolonged bleeding time on univariate analysis. On multivariate analysis, both tumour size > 5 cm in diameter and a Child-Pugh's grading C (odd's ratio, 95% confidence interval and P value were measured as 38.5, 2.8-534.7, < 0.001, and 10.5, 0.9-117.6, 0.02, respectively) were the significant independent predictors. A significant correlation existed between tumour diameter and bleeding time (r = 0.44, P < 0.01). In conclusion, these results suggest that prolonged bleeding time may be categorized as a new clinical manifestation in patients with HCC. In addition to cirrhosis, HCC itself may also participate in the pathogenesis of bleeding time prolongation.

Targeting of the catalytic subunit of protein phosphatase-1 to the glycolytic enzyme phosphofructokinase

In this study, we demonstrate that the catalytic subunit of rabbit muscle protein phosphatase-1 (PP1) binds to muscle phosphofructokinase (6-phosphofructo-1-kinase, PFK). A protein of 85 kDa was isolated from rat muscle by affinity chromatography on PP1-Sepharose and was identified as phosphofructokinase by partial amino acid sequence analysis. This novel finding of a protein-protein interaction between PP1 and PFK was confirmed by reciprocal experiments in which the binding of PP1 to PFK-agarose was demonstrated. Elution of PP1 from PFK-agarose was maximal at ca. 0.4 M NaCl. The specificity of binding was demonstrated by isolation of PP1 from a partially purified rabbit muscle PP1 preparation. All four known isoforms of PP1 (PP1alpha, PP1gamma1, PP1gamma2, and PP1delta) were shown to bind to PFK-agarose. The activity of PP1 was only partially inhibited by PFK. The preformed complex between PP1 and PFK did not bind to inhibitor-2-Sepharose. The stoichiometry of binding of PP1 to the PFK monomer was found to be 1:1 in the isolated PP1.PFK complex. An interaction between PP1 and PFK in muscle extracts was demonstrated by their coimmunoprecipitation. Our findings raise the interesting possibility that PP1 may be targeted to PFK, and may be physiologically relevant in the context that PFK and other glycolytic enzymes have been shown to be micro-compartmentalized by binding to F-actin. This in turn points to a role for PP1 in control of glycolytic flux by protein phosphorylation-dephosphorylation mechanisms.

Mutational analysis of substrate recognition by protein phosphatase 1

The role of residues that are involved in substrate recognition by rabbit muscle protein phosphatase 1alpha (PP1) was investigated by site-directed mutagenesis and kinetic analyses using phosphorylase a, RII peptide, Kemptide, and p-nitrophenyl phosphate as substrates. The atomic structure of PP1 has shown the active site to be at the confluence of three shallow grooves, a C-terminal groove, an acidic groove, and a hydrophobic groove. Mutations of residues D208, D210, D212, E218, D220, E252, D253, E256, E275, and D277 in the acidic groove, of R221, W206, and Y134, which have been suggested to be involved in substrate binding, and of residues C127, I130, and D197 in the hydrophobic groove were examined. Our results show that mutations in the acidic groove lead to modest changes in substrate binding, consistent with a role of the acidic residues in forming a negatively charged surface well for binding of peptides with basic N-termini. Severe effects on Vmax were observed for mutants of R221, D208, and W206. These results are consistent with the proposal that the R221 plays an important role as a phosphate oxygen ligand that positions the substrate for catalysis. The kinetic behavior of mutants at W206 and D208 can be explained by the observation that, together with R221, these residues form the microenvironment which dictates the orientation of the imidazole ring of H248, one of the metal binding ligands, as well as contributing to the orientation of R221 itself.

Mutagenesis of the L7 loop connecting beta strands 12 and 13 of calcineurin: evidence for a structural role in activity changes

Calcineurin is a heterodimer consisting of a catalytic A-subunit and a B-subunit, and is regulated by binding of calmodulin and calcium. The C-terminus of the A-subunit contains an autoinhibitory domain which plays an important role in regulation of calcineurin activity. In this study, we have mutated the L7 loop connecting beta strands 12 and 13 in calcineurin A. These mutants included two chimeric mutants in which a four amino acid stretch in the cognate L7 loops of the related proteins phosphatase-1 (GEFD) or -2A (YRCG) were substituted for the calcineurin sequence DVYN (313-316), a point mutation (L312C), and a truncated mutant in which the YRG sequence replaced residues 313-316. Examination of the activities of these mutants led to the striking finding that truncation of the loop region by one residue resulted in hyperactivation of the calcineurin A-subunit. That the hyperactivation is due to conformational effects on the catalytic core of the enzyme was established since this effect was maintained in truncation mutants (at residues 456 and 388) in which the calmodulin and autoinhibitory domains were deleted. These studies provide evidence that the L7 loop is an important structural element in the conformation of the active site, and may participate in the conformational transitions of calcineurin between a catalytically repressed state and an activated state under the influence of the B-subunit.

Conversion of protein phosphatase 1 catalytic subunit to a Mn(2+)-dependent enzyme impairs its regulation by inhibitor 1

The phosphorylase phosphatase activity of protein phosphatase 1 (PP1) catalytic subunit from freshly purified rabbit skeletal muscle was inhibited by MnCl2. Prolonged storage or inhibition by nonspecific phosphatase inhibitors ATP, sodium pyrophosphate, and NaF converted the muscle PP1 to a form that required Mn2+ for enzyme activity. Recombinant PP1 catalytic subunit expressed in Escherichia coli was also a Mn2+-dependent enzyme. While native PP1 was inhibited by the phosphoprotein inhibitor I (I-1), with an IC50 of 1 nM, 40-50-fold higher concentrations of I-1 were required to inhibit the Mn2+-dependent PP1 enzymes. Conversion to the Mn2+-dependent state was accompanied by a 20-fold increase in PP1's ability to dephosphorylate and inactivate I-1. Inhibition by thiophosphorylated I-1 established that dephosphorylation does not play a significant role in I-1's reduced potency as an inhibitor of Mn2+-dependent PP1. The Mn2+-dependent PP1 enzymes were poorly inhibited by N-terminal phosphopeptides of I-1, indicating their impaired interaction with the I-1 functional domain. Mutation of a residue conserved in I-1 and DARPP-32, a structurally related PP1 inhibitor, preferentially attenuated I-1's activity as an inhibitor of Mn2+-dependent PP1. These data showed that, in addition to changes in its catalytic properties, Mn2+-dependent PP1 was modified in its interaction with I-1 at a site that was distinct from its catalytic domain. Our studies suggest that conversion to a Mn2+-dependent state alters multiple structural elements in PP1 catalytic subunit that together define its regulation by I-1.

Gall-bladder wall thickening in patients with liver cirrhosis

Gall-bladder wall thickening is commonly seen in patients with cirrhosis, but its exact causes have not been well established. We evaluated clinical, biochemical and haemodynamic data of patients with cirrhosis with respect to the presence of thickening of the gall-bladder wall. After excluding patients who presented with gallstones, acute or chronic cholecystitis, heart failure, a serum creatinine level greater than 2 mg/dL and/or a serum alanine aminotransferase level greater than 400 U/L, 77 patients with cirrhosis (75 male, two female; mean age 58 +/- 8 years) were enrolled in the study. Clinical, biochemical, ultrasound and haemodynamic data were obtained in every patient. Forty-one (53%) of 77 patients with cirrhosis had gall-bladder wall thickening (> 4 mm). Compared with patients with a normal gall-bladder wall, patients with gall-bladder wall thickening had significantly lower serum albumin levels (3.6 +/- 0.6 vs 2.9 +/- 0.7 gm/dL, respectively; P < 0.05), a longer prothrombin time (13 +/- 6 vs 16 +/- 6 s, respectively; P < 0.05), more patients with Child-Pugh class C (6 vs 37%, respectively; P < 0.05) and more patients with ascites (8 vs 50%, respectively; P < 0.05). In addition, compared with patients with a normal gall-bladder wall, those patients with gall-bladder wall thickening had a higher hepatic venous pressure gradient (13.9 +/- 4.5 vs 17.1 +/- 4.1 mmHg, respectively; P < 0.01) and a lower systemic vascular resistance (SVR; 1144 +/- 332 vs 1010 +/- 318 dyn.s/cm5, respectively; P < 0.05). Using a multivariate analysis, the presence of ascites and SVR lower than 900 dyn.s/cm5 were independently correlated with the presence of gall-bladder wall thickening, while a hepatic vein pressure gradient greater than 10 mmHg had only a marginally significant association. The presence of ascites, decreased SVR and portal hypertension are related to the occurrence of gall-bladder wall thickening in patients with cirrhosis, indicating that the development of gall-bladder wall thickening may be multifactorial.

Age-related changes of VIP, NPY and somatostatin-immunoreactive neurons in the cerebral cortex of aged rats

Recent studies have explored certain changes with aging of neurons containing neuropeptides. The degree of loss of vasoactive intestinal polypeptide (VIP)-, neuropeptide Y (NPY)- and somatostatin-containing neurons in the aged CNS has not yet been established with certainty however, and available data is often contradictory. Changes with aging of VIP- and NPY-containing neurons were demonstrated by immunocytochemistry in this study. A major loss of VIP-immunoreactive (ir) neurons in aged rat brain was observed in the frontal cortex area 3, parietal cortex area 1, hindlimb area, temporal cortex area 1 and 2, monocular part of occipital cortex area 1, occipital cortex area 2, and retrosplenial cortex. VIP-ir cells in the frontal cortex areas 1 and 2, parietal cortex area 2, forelimb area, binocular part of the occipital cortex area 1, and the dentate gyrus were moderately decreased. The axis of VIP neurons in the aged group showed an irregular orientation tendency, especially in layers II and III. Major loss of NPY-ir neurons in aged rat brain were observed in the retrosplenial cortex, frontal cortex areas 1 and 2, parietal cortex areas 1 and 2, occipital cortex areas 1 and 2, the temporal cortex, hippocampus proper and cingulate cortex. Loss of NPY-ir neurons was observed mostly in layers V and VI. The number and length of dendritic branches also appeared to have decreased and shortened in the aged group. There were only slight decreases of somatostatin-ir cell numbers in the parietal and occipital cortex of the aged group. These results indicate the involvement of VIP and NPY-ir neurons in the aging process of cerebral cortex, and provide the morphological evidence for the decreased number of VIP and NPY neurons by immunocytochemistry in each area of cerebral cortex of aged rats.

Expression and reconstitution of calcineurin A and B subunits

Calcineurin consists of two subunits, a catalytic A subunit of 60 kDa and a regulatory B subunit of 19 kDa. Both the A and B subunits of rat brain calcineurin were expressed in E. coli. The B-subunit was readily overexpressed in the pET-21a vector with yields of > 70 mg of purified B subunit per 1 culture, representing > 17% of the soluble E. coli protein. About 8 mg of purified A subunit was obtained. The enzyme activities of the A-subunit and the reconstituted AB complex were found to be comparable to that of the bovine brain enzyme. The reconstitution of the AB complex was studied and shown to be rapid.

Genes in the RB pathway and their knockout in mice

The retinoblastoma susceptibility gene (RB), the first identified human tumor suppressor gene, has been shown to be directly involved in the genesis of a variety of human cancers. RB is actually one of a family of three closely related genes including p107 and p130. Many elegant biochemical studies have demonstrated that RB is a critical component of the cell cycle regulatory machinery and have characterized the downstream effectors which the RB gene product regulates. More recent advances have demonstrated that the function of RB and RB-related genes is positively and negatively regulated by an intricate network of cell cycle regulatory proteins, some of which have also been implicated as tumor suppressor genes. Despite the detailed understanding of these biochemical and genetic pathways, the full function of genes in the RB pathway in the context of a whole organism is only now being addressed. Using gene knockout technology, it is now known that RB, and RB-related proteins p107 and p130, have important functions during early mouse development. Furthermore, despite its ubiquitous expression, RB has tissue- and cell-type specific effects which account for its function as a tumor suppressor but may also be independent of its role as a cell cycle regulator. Analysis of mice lacking regulatory genes upstream of RB and effector genes downstream of RB have confirmed that other genes in this pathway have tissue-specific effects on development and tumor susceptibility in mice.

Effect of activation of protein phosphatase 1 on sulfhydryl reactivity

Myofibril protein phosphatase 1 (PP1) from bovine heart, identified as PP1alpha, was purified in a latent form which was dependent on Co2+ or Mn2+ for activity (Y. Chu, S. E. Wilson, and K. K. Schlender (1994) Biochim. Biophys. Acta 1208, 45-54). This was also true for recombinant PP1 alpha expressed in Escherichia coli (Z. Zhang, G. Bai, S. Deans-Zirattu, M. F. Browner, and E. Y. C. Lee (1992) J. Biol. Chem. 267, 1484-1490). Here we report on the change in the sulfhydryl reactivity during the cation activation process. The activation of myofibrillar PP1 by Co2+ was prevented by 10 mM dithiothreitol (DTT) and incubation of the Co2+-activated enzyme with 50 mM DTT reversed the activation. Activation of recombinant PP1alpha was associated with 57Co2+ incorporation into PP1. DTT reversal of Co2+-activated PP1 was accompanied by release of Co2+ from the enzyme. The latent PP1 modified with 2-nitro-5-thiocyanobenzoic acid (NTCB) or N-ethylmaleimide (NEM) did not bind Co2+ and could not be activated by Co2+. Conversely, the Co2+-activated PP1 was resistant to inactivation with NTCB and less sensitive to NEM. Similarly, PP1 pretreated with NTCB was not activated by Mn2+ and the Mn2+-activated enzyme was also resistant to NTCB inhibition. The number of sulfhydryls of nondenatured PP1, reactive with 5, 5'-dithiobis[2-nitrobenzoic acid] (DTNB), was reduced from approximately 8 to 2-3 mol/mol when the enzyme was activated with Co2+ or Mn2+. After denaturation with guanidine-HCl, the number of reactive sulfhydryls of nonactivated PP1 and Co2+-activated PP1 was approximately 10 mol/mol enzyme. These results suggest that when PP1 is activated by Co2+ or Mn2+, the enzyme undergoes a conformational change resulting in some of the cysteine sulfhydryls no longer being accessible to chemical modification.

Dietary sodium intake modulates pituitary proopiomelanocortin mRNA abundance

The pituitary prohormone proopiomelanocortin gives rise to melanocortins of alpha, beta, and gamma primary structure in addition to corticotropin. Melanocortins have a variety of actions in mammals, and each is natriuretic. In particular, gamma-melanocyte-stimulating hormone has been shown to mediate reflex natriuresis after acute unilateral nephrectomy. We examined whether this peptide could play a role in longer term adjustments in sodium balance by measuring plasma gamma-melanocyte-stimulating hormone and corticotropin concentrations, as well as pituitary proopiomelanocortin mRNA abundance, in Sprague-Dawley rats ingesting either a low (0.07% NaCl) or high (7.5% NaCl) sodium diet. One week after the high sodium diet, plasma gamma-melanocyte-stimulating hormone concentration was double the value seen in rats on the low sodium diet (158 +/- 5 [SE] versus 76 +/- 9 fmol/mL, P < .001), a change that was accompanied by a fivefold increase in plasma atrial natriuretic peptide concentration but no change in plasma corticotropin. Whole pituitary proopiomelanocortin mRNA abundance, measured with a probe to exon 3 of the rat proopiomelanocortin gene, was significantly increased after 1 week of the high sodium diet compared with the low sodium diet and increased further at 2 and 3 weeks. This increase occurred primarily in the neurointermediate lobe as demonstrated by in situ hybridization; the content of gamma-melanocyte-stimulating hormone immunoreactivity was also increased in this lobe, but not the anterior lobe, after 1 week of the high sodium diet. These results demonstrate that high dietary sodium intake increases neurointermediate lobe proopiomelanocortin mRNA abundance compared with a very low sodium diet and also suggest that proopiomelanocortin is preferentially processed into gamma-melanocyte-stimulating hormone rather than corticotropin. These observations consequently raise the possibility of a role for this peptide hormone system in the adjustments to a high salt diet.

Expression and mutation of H-ras in uterine cervical cancer

In cervical cancer, abnormalities of ras genes have not been fully investigated. We studied the expression and mutation of H-ras oncogene in cervical cancer to investigate their relationship and usefulness as an independent prognostic indicator. Twenty-seven paraffin-embedded resection specimens of cervical cancer (21 squamous, 3 adeno, 2 adenosquamous, and 1 small cell) were examined by immunohistochemistry using a mAb H-ras p21 and by PCR and allele-specific oligonucleotide hybridization using H-ras codon 12 and 61 amplimers and oligonucleotide probes. A strong immunoreaction was noted in 10 cases (37%) and weak immunoreaction in an additional 6 cases (22%). H-ras codon 12 mutations were detected in 6 of 27 cases (22%) and all of the mutations were guanine to adenine transitions. There was no mutation in codon 61. Cases with codon 12 mutations included all 3 squamous, 2 adeno, and I adenosquamous carcinoma. Only 3 of 16 (19%) cases with positive staining and 3 of 11 (27%) cases with negative staining showed mutations. No correlation was found between ras gene alterations and patient survival time. Our findings indicate that expression and mutation of H-ras oncogene occur in cervical cancer but their determination adds no useful prognostic information.

Phosphodiesterase activity as a mediator of renal resistance to ANP in pathological salt retention

Resistance to the natriuretic action of atrial natriuretic peptide (ANP) is a hallmark of states of pathological sodium retention including congestive heart failure, cirrhosis of the liver, and nephrotic syndrome. A variety of mechanisms including reduced delivery of filtrate to ANP-sensitive sites in the inner medullary collecting duct and diminished receptor density in this tubular segment have been offered to account for this resistance. Recent studies in experimental nephrotic syndrome and in liver disease produced by ligation of the common bile duct in rats suggest that increased activity of cyclic guanosine 3',5'-monophosphate (cGMP) phosphodiesterase may be an important mediator of renal resistance to ANP. Such increased enzyme activity rapidly catabolizes the second messenger cGMP, normally formed when ANP interacts with its biologically active natriuretic peptide A receptors, thereby leading to blunted ANP responsiveness. This increased phosphodiesterase activity offers a novel approach to the management of clinical conditions associated with sodium retention and edema formation.