Cystic fibrosis transmembrane regulator mRNA expression relative to ion-nutrient transport in spontaneously differentiating human intestinal CaCo-2 epithelial cells

The relative abundance of cystic fibrosis transmembrane regulator (CFTR) message at various stages of postconfluence development was compared with evolving cellular ion-nutrient transport properties of CaCo-2 human intestinal cells. Initially these cells demonstrate electrogenic Cl secretion manifested by secretagogue-induced changes in short-circuit current. Over time, however, the secretory characteristics of CaCo-2 monolayers diminish, and brush border hydrolase activities and glucose-dependent and amiloride-sensitive Na transport increase. With a polymerase chain reaction-derived cDNA probe to CFTR exon 13, two distinct mRNA transcripts of 6.5 and 4.3 kb were found. No significant differences in their abundance were noted in cells at 6 and 28 days after confluence. These data suggest two possible interpretations for the role of CFTR protein. First, if CFTR is membrane Cl channel, its protein expression or activity could be differentially regulated during CaCo-2 cell development. Alternatively, CFTR may not be a Cl channel but may serve as an important regulatory membrane protein.

Lymphocyte abnormalities in the BB rat

The BB rat has a marked T cell lymphocytopenia, with a near absence of peripheral "helper" T cells recognized by monoclonal antibody W3/25 (W3/25+ T cells). The lymphocytes of the BB rat's spleen and thymus were examined for the presence of W3/25+ T cells, which were found to be absent in the spleen but present in normal amounts in the thymus. Concanavalin A (Con A) responsiveness was absent in the BB's peripheral blood and spleen but present in the thymus. Thus, in these three lymphoid compartments, Con A responsiveness directly correlated with the presence or absence of W3/25+ T cells. These lymphocyte abnormalities in the BB rat are notably different from lymphocyte changes present in human type I diabetes.

Kallikrein-induced uterine contraction independent of kinin formation

Responses of smooth muscle to kallikreins (EC 3.4.21.8) are generally considered to result from kinin formation. This premise was reexamined with the isolated rat uterus. Rat urinary kallikrein or bradykinin produced dose-dependent contractions of rat uterus but kallikrein was 5-fold more potent than bradykinin. Kallikrein caused an immediate series of rhythmic contractions which could be increased gradually with subsequent addition of kininogen substrate. Kallikrein-induced contractions were unaffected by carboxypeptidase B or a bradykinin antiserum whereas bradykinin-induced contractions were attenuated or abolished. Other serine proteinases, including trypsin, either did not induce contraction in the absence of added kininogen or did so minimally. Although small amounts of kininogen-like substrate were found in uterine tissue, detectable kinin levels (greater than 4 pg) could not be found in bathing media during maximal kallikrein-induced contractions or after uterine tissue was incubated with high concentrations of the enzyme in the presence of SQ 20881, a kininase II inhibitor. The data suggest that uterine contraction produced by a homologous kallikrein does not involve kinin formation but results from an action of this serine proteinase upon other accessible systems coupled to the contractile response.

Hyperinsulinemic hypoglycemia: effect of epinephrine suppression

The inhibitory effect of epinephrine on basal and tolbutamide-stimulated insulin release was studied in 5 patients with hyperinsulinemic hypoglycemia. Epinephrine inhibited both basal and tolbutamide-induced insulin release in patients with beta-cell adenoma and hyperplasia, but failed to inhibit insulin release in a patient with beta-cell carcinoma. The inhibition of basal insulin with epinephrine was maximum in patients with beta-cell hyperplasia. This differential inhibitory effect of epinephrine on insulin release may prove to be a useful screening test in the preoperative diagnosis of the nature of the lesion producing hyperinsulinemia.

Effect of free fatty acids and insulin on protein synthesis and amino acid metabolism of isolated rat diaphragms

The effect of free fatty acids and insulin on the incorporation of C-14 from amino acids into muscle proteins was studied in vitro using “cut” or “intact” rat diaphragms.

Insulin promoted the incorporation of C-14 from L-gly-cine-2-C-14, L-histidine-2-ring-C-14 and L-leucine-U-C-14 into muscle proteins. Insulin stimulated the uptake of 0.05 mM. leucine-U-C-14 from the medium, but not its oxidation to C-14-O2.

Palmitate (3 mM.) decreased the incorporation of C-14 from glycine and histidine into proteins of muscles stimulated with insulin. Octanoate (0.5-3 mM.) decreased the incorporation of C-14 from leucine into proteins. The inhibitory effect of octanoate on protein synthesis was demonstrated in the presence or absence of glucose and/or insulin. DL-β-hydroxybutyrate (15 mM.) decreased the incorporation of C-14 from leucine-U-C-14 into proteins in the presence of insulin.

Octanoate (1 mM.) stimulated the uptake of C-14 from leucine-U-C-14 from the medium and its oxidation to C-14-O2. DL-β-hydroxybutyrate (15 mM.) appeared to inhibit both processes, however; the latter may be due to isotope dilution.

The nonutilizable amino acid, α-aminoisobutyric acid-C-14, penetrated less readily into the intracellular water of diaphragms incubated with 1 mM. octanoate than into controls. However, since octanoate stimulated the uptake of C-14 from leucine from the medium it appears likely that octanoate inhibited the incorporation of C-14 from leucine into proteins at a step beyond amino acid transport.

It is suggested that FFA can influence amino acid metabolism in muscles and decelerate their incorporation into proteins. Limitation of protein synthesis in muscle by increased intracellular FFA may contribute to the supply of amino acids available for neoglucogenesis during stress and carbohydrate deprivation.

Effect of human serum albumin on the glucose metabolism of isolated rat diaphragm and its response to insulin

The effect of human serum albumin prepared by Cohn method 6 on the glucose metabolism of isolated rat diaphragms was studied. In the absence of insulin 5 per cent albumin slightly inhibited glucose uptake and lactate production but not glycogen synthesis. Albumin partially inhibited the stimulatory effect of insulin on glucose uptake, lactate production and glycogen synthesis. The insulin antagonistic effect of 5 per cent albumin was due in part only to increased H+ ion concentration in the medium. Albumin (1.25 per cent) did not affect glucose utilization or lactate production with or without insulin. Albumin (5 per cent) alone slightly but significantly augmented the penetration of d-xylose into “intact” diaphragms. In the presence of insulin and albumin the space of distribution of d-xylose was significantly less than with insulin alone.

The albumin preparations contained free fatty acids and citrate; however, the insulin antagonism of 5 per cent albumin could not be reproduced with palmitate or citrate. Following dialysis and lyophilization 5 per cent albumin assayed at controlled pH did not affect glucose uptake, lactate production or glycogen synthesis either in the presence or absence of insulin. The noninhibitory albumin was extracted with TCA-ethanol, dialyzed, lyophilized and assayed as above. It significantly inhibited the stimulatory effect of insulin on glucose uptake, lactate production and glycogen synthesis.

It is suggested that several factors can be associated with albumin and antagonize the stimulatory effect of insulin on muscles in vitro. These factors will have to be separated and characterized before the biological significance of the “synalbumin antagonist” of insulin can be evaluated.