Cyclic AMP stimulation of amino acid uptake in bone and kidney

Effect of parathyroid hormone on amino acid transport by cultured neonatal mouse calvarial bone cells

The effect of synthetic bovine parathyroid hormone [bPTH-(1-34)] on amino acid uptake by confluent primary cultures of osteoblast-like cells isolated from neonatal mouse calvaria was studied. The uptake of proline and leucine by membrane transport Systems A, ASC, and L was discriminated on the basis of their sodium dependency and sensitivity to the system-specific amino acid analogs 2-(methylamino)-isobutyric acid (MeAIB) for System A and 2-amino-(2,2,1)-heptane-2-carboxylic acid (BCH) for System L. Treatment with 24 nM bPTH-(1-34) in serum-free EBSS for 4 hr increased the initial uptake rate of proline by 50-80% but had no effect on the uptake of leucine. Temporally, the increase in proline uptake was preceded by a 2-hr lag period and plateaued after 5-6 hr. A 5-min exposure to the hormone was sufficient to cause a significant increase in proline uptake measured 4 hr later. The magnitude of the increase was dose-related from 0.24 to 240 nM bPTH-(1-34), with the half-maximal effect occurring at 2.4 nM. Only the sodium-dependent, MeAIB-inhibitable component of proline uptake was elevated. Eadie-Hofstee analysis indicated that bPTH-(1-34) increased Vmax without changing the Km. Actinomycin D and cycloheximide prevented the hormone-stimulated increase, suggesting that RNA and protein synthesis were required. Treatment with either inhibitor alone caused a 30-35% decrease in proline transport that was not observed in the presence of bPTH-(1-34), indicating an effect not dependent on macromolecular synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of calcium in stimulation of sugar transport in muscle by lithium

We have investigated the relation between the stimulation of sugar transport by Li+ and Li+-induced changes in cellular Ca2+ distribution. The fluxes of 3-O-[14C]methyl-D-glucose and 45Ca were measured in hemidiaphragm, soleus, and cardiac muscles of the rat, and cellular levels of Ca2+, Na+ and K+ were determined. Li+ increased in parallel the fluxes of 3-O-[14C]methyl-D-glucose and 45Ca in rat hemidiaphragm and soleus muscles. Sugar transport and Ca2+ efflux were also stimulated by Li+ in Ca2+-free medium, suggesting that in addition to increasing sarcolemmal Ca2+ influx, Li+ may also cause the release of Ca2+ from intracellular storage sites, presumably the mitochondria. Mitochondria were isolated from preparations of rat ventricular muscle exposed to Li+, and their Ca2+ content was determined. In rat cardiac muscle, Li+ stimulation of sugar transport was associated with decreased mitochondrial Ca2+ levels (indicating mitochondrial Ca2+ release) only under conditions of deteriorating mitochondrial function. Thus, Li+-induced changes in cellular Ca2+ distribution, which would increase cytosolic Ca2+ levels, were associated with stimulation of sugar transport. These observations support the hypothesis that the increased availability of cytosolic Ca2+ regulates the activity of the sugar transport system in muscle.

Effects of amino acids, glucagon, insulin and acetylcholine on cyclic nucleotide metabolism and amylase secretion in isolated mouse pancreatic fragments

The effects of amino acids, exogenous islet hormones and acetylcholine on cyclic nucleotide metabolism and amylase secretion in the isolated mouse pancreas have been investigated. The changes in levels of adenosine 3',5'-cyclic monophosphate (cyclic AMP) and guanosine 3',5'-cyclic monophosphate (cyclic GMP) were measured at different times during exposure of pancreatic fragments to amino acids (L-alanine and L-arginine), islet hormones (insulin and glucagon) or acetylcholine (ACh). L-Alanine (1-20 mM) evoked a transient increase in cyclic AMP concentration accompanied by an initial decrease and subsequent increase in the tissue concentration of cyclic GMP. L-Arginine (1-20 mM) induced a complex triphasic change in cyclic AMP concentrations involving an initial rise and a delayed sustained elevation. The changes in levels of cyclic GMP increased only transiently. The effects of insulin (10(-6) M) and to some extent glucagon (5 X 10(-7) M) resembled those seen with L-arginine. The effects of amino acids and islet hormones were all dose-dependent. ACh (10(-7) M) elicited a marked reduction in cyclic AMP concentration and this was accompanied by a concomitant increase in the level of cyclic GMP. The amino acids and the islet hormones had no significant effect on amylase secretion whereas ACh, of course, evoked a large increase in amylase output. The results with the amino acids and islet hormones reveal a clear dissociation between cyclic nucleotide changes and amylase secretion and further suggest that the marked reciprocal changes in cyclic AMP and cyclic GMP concentrations may constitute an important physiological role for the cyclic nucleotides to regulate amino acid transport in the pancreas.

Effects of dibutyryl cyclic AMP on the transport of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid in separated tubules and brush border membranes from rabbit kidney

The effect of dibutyryl cyclic AMP on the transport of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid in separated tubules and purified brush border membranes from rabbit kidney was investigated using a rapid filtration procedure. Dibutyryl cyclic AMP stimulated the uptake of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid by separated renal tubules in agreement iwth prior studies utilizing renal slices (Rea, C. and Segal, S. (1973) Biochim. Biophys. Acta 311, 615--624; Weiss, I.W., Morgan, K. and Phang, J.M. (1972) J. Biol. Chem. 247, 760--764). However, in contrast to previous reports, no preincubation of the tissue with dibutyryl cyclic AMP was required for stimulation of transport to be manifest. Dibutyryl cyclic AMP stimulated oxygen consumption by separated tubules suggesting that stimulation of transport may occur by a linkage with renal oxidative metabolism. Dibutyryl cyclic AMP increased the uptake of alpha-aminoisobutyric acid into purified renal brush border membranes. However the uptakes of alpha-methyl-D-glucoside, proline, leucine and phosphate into brush border membranes were significantly inhibited.

Dicarboxylic amino acid uptake in normal, Friedreich's ataxia, and dicarboxylic aminoaciduria fibroblasts

Glutamic and aspartic acid uptake was measured in skin fibroblasts from patients with Friedreich's Ataxia, dicarboxylic aminoaciduria, and normal individuals. The results showed no difference in uptake kinetics of either dicarboxylic amino acids between Friedreich's Ataxia and normal cells, but reduced uptake velocities in dicarboxylic aminoaciduria fibroblasts. Friedreich's Ataxia fibroblasts were, however, less calcium-dependent and more magnesium and phosphate-dependent than controls in glucose-free incubation mixture. This difference might be related to some degree of glucose intolerance by Friedreich's Ataxia fibroblasts in culture.

Immuno-histochemical localization of cyclic nucleotides in mineralized tissues: mechanically-stressed osteoblasts in vivo

Previous experiments indicate that bone cells respond to external stimuli with fluctuations of cyclic nucleotide levels. The objective of this experiment was to study the response of alveolar bone to the application of tensile forces through an examination of the osteoblastic staining pattern for cAMP and cGMP. Cat canines were tipped by 80-g force for 0 to 48 hours. Fresh frozen, unfixed, undecalcified jaws were sectioned sagittally and stained immuno-histochemically for cAMP and cGMP. In tension sites, osteoblastic staining intensity for cAMP decreased gradually from one to three hours, and then increased by 24 hours. Intense staining for cGMP, visible in osteoblasts of all treated cats, peaked after three hours of treatment and then again at 24 hours. Generally, groups of cGMP-stained osteoblasts were found adjacent to unstained osteoblasts. The observed fluctuations in the osteoblasts staining pattern for cAMP and cGMP indicates involvement of these substances in the early response of osteoblasts to mechanical stimuli in vivo.

Isoproterenol-stimulated taurine influx in the perfused rat heart

Taurine influx in the perfused rat heart was characterized and the effect of isoproterenol on this process determined. Hearts were perfused by the Langendorff technique with [3H]-taurine in a non-recirculating system. The rate of taurine influx was constant for at least 20 min and the process was saturable. A Km of 45 micron indicated that taurine influx is mediated by a high affinity transport system. Competition between taurine and beta-alanine, but not alpha-amino acids, for influx indicated that the transport sites are specific for beta-amino acids. Isoproterenol (4 X 10(-7) M) stimulated the rate of taurine influx, but propranolol (1 X 10(-8) M) blocked this stimulation. The enhancement of influx by isoproterenol was specific for beta-amino acids in that alpha-amino acid influx was not affected. Dibutyryl cyclic AMP (1 X 10(-3) M) and theophylline (1 X 10(-3) M) also stimulated taurine influx, whereas alterations in heart rate had no effect on the rate of taurine influx. The results are suggestive of a beta-adrenergically activated, cyclic AMP-mediated mechanism controlling isoproterenol-stimulated taurine influx.

Inhibition by cyclic AMP and dibutyryl cyclic AMP of transport of organic acids in kidney cortex

1. Cyclic adenosine 3',5'-monophosphate and N-6-2'-O-dibutyryl cyclic adenosine 3',5'-monophosphate decrease the initial entry rate and the steady-state uptake of p-aminohippurate and uric acid by rabbit kidney cortex slices. 2. N-6-2'-O-Dibutyryl adenosine 3'-5'-monophosphate inhibits the tubular transport of p-aminohippurate competitively. 3. Isoproterenol, known to increase cyclic nucleotide concentration of the cortical tubules by activation of adenyl cyclase, decreases p-aminohippurate transport. Antidiuretic hormone which is known to stimulate only medullary adenyl cyclase has no effect on p-amino-hippurate uptake by cortical slices. 4. Theophylline, which inhibits cyclic nucleotide phosphodiesterase and, therefore, enhances the cellular accumulation of endogenous cyclic nucleotide, depresses p-aminohippurate transport.

Transport of methionine and proline by rat liver slices and the effect of certain hormones

1. Transport characteristics of l-methionine and l-proline in rat liver slices in vitro were studied. 2. Intracellular concentration gradients for methionine were obtained. 3. Methionine uptake was inhibited by iodoacetate, dinitrophenol, Na(+)-free media and also by glycine, lysine, cysteine and dithiothreitol but not by alpha-aminoisobutyrate. 4. The rate of methionine metabolism in the slice was slow. 5. Puromycin inhibited methionine incorporation into protein, but not methionine uptake. 6. Methionine inhibited the transport of alpha-aminoisobutyrate but not of cystine. 7. Efflux and exchange diffusion of methionine was studied. 8. Amino acid transport in rat liver slices was not affected by thyroidectomy. 9. Addition of insulin, glucagon, adrenaline or cortisol did not affect the transport of methionine. 10. Addition of 6-N,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate increased methionine transport after a 120min incubation period in some experiments. 11. Studies of l-proline transport were invalidated because of the rapid evolution of CO(2) from the substrate.

Cyclic adenosine 3',5'-monophosphate concentration in the pancreas following stimulation by secretin, cholecystokinin-pancreozymin and acetylcholine

1. Following an I.V. injection of secretin into anaesthetized cats, the pancreatic cyclic AMP concentration rose within 30 sec and reached near-maximal values within 1 min. Pancreatic secretion began only after 45 sec. As secretion declined, the cyclic AMP concentration also fell. However, after 40 min, when secretion had ceased, the concentration again rose, reaching a maximum after about 80 min and returned to basal values within 140 min.2. During secretin infusion the pattern of cyclic AMP changes was the same, except that the initial rise was maintained as long as secretin was infused.3. Following either pancreozymin or acetylcholine, alone or super-imposed on secretin stimulation, similar changes in cyclic AMP concentration were observed. However, the initial rise lasted only 30 sec, basal concentrations being approached within 1 min, and was accompanied by enzyme secretion. The concentration of cyclic AMP subsequently rose and fell again, in the absence of enzyme secretion, exactly as after secretin stimulation.4. Similar observations were made using an isolated, saline-perfused preparation of the cat's pancreas.5. By using very low doses of pancreozymin it was possible to observe the first rise in cyclic AMP concentration in the absence of enzyme secretion. Similarly atropine, while blocking enzyme secretion, did not affect the rise in cyclic AMP concentration after acetylcholine. The second increase in concentration was never associated with secretion (it may have been connected with the synthesis of exportable enzymes by the gland).6. While these observations suggest that cyclic AMP may be involved in the response of the pancreas to secretin, pancreozymin and acetylcholine, no simple relation exists between cyclic AMP concentration and secretion.