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PubMed1992

Characterization of the Streptococcus mutans GS-5 fruA gene encoding exo-beta-D-fructosidase.

The complete nucleotide sequence (5,010 bp) of the fructanase gene (fruA) and flanking regions of the chromosome of Streptococcus mutans GS-5 was determined. The fruA gene appears to be the sole transcript arising from a proximal promoter. The presumed precursor of the secreted FruA protein consists of 1,423 amino acids, and it has an M(r) of 158,656 and a pI of 4.82. The N terminus of FruA has characteristics in common with signal peptides of gram-positive organisms. The C terminus consists of a serine- and threonine-rich region, followed by the peptide LPDTGD, 4 charged amino acids, 21 amino acids with a strongly hydrophobic character, and a charged pentapeptide tail, which are proposed to correspond to the wall-spanning region, the LPXTGX consensus sequence, and the membrane-spanning domains of surface-associated proteins of gram-positive cocci. The FruA protein has significant homology with the Bacillus subtilis levanase (SacC), the Bacteroides fragilis levanase (ScrL), yeast invertases, and a number of other beta-fructosidases but not with fructosyltransferase, glucosyltransferases, or glucan-binding proteins of oral streptococci. Genes with homology to fruA were detected in S. mutans serotype c, e, and f strains, Streptococcus rattus, Streptococcus salivarius, and Streptococcus sanguis. A deletion derivative of FruA lacking the C-terminal 437 amino acids was still functional and could hydrolyze beta-(2,6)- and beta-(2,1)-linked sugars, but with altered preference for substrates. The data begin to define functional domains of the FruA protein and potential regulatory sites for induction, repression, growth rate control, and posttranslational localization of this multifunctional enzyme.

Amino Acid Sequence↗

PubMed1994

Potassium extrusion by the moderately halophilic and alkaliphilic methanogen methanolobus taylorii GS-16 and homeostasis of cytosolic pH.

Methanolobus taylorii GS-16, a moderately halophilic and alkaliphilic methanogen, grows over a wide pH range, from 6.8 to 9.0. Cells suspended in medium with a pH above 8.2 reversed their transmembrane pH gradient (delta pH), making their cytosol more acidic than the medium. The decreased energy in the proton motive force due to the reversed delta pH was partly compensated by an increased electric membrane potential (delta psi). The cytosolic acidification by M. taylorii at alkaline pH values was accompanied by K+ extrusion. The cytosolic K+ concentration was 110 mM in cells suspended at pH 8.7, but it was 320 mM in cells suspended at neutral pH values. High external K+ concentrations (210 mM or higher) inhibited the growth of M. taylorii at alkaline pH values, perhaps by preventing K+ extrusion. Cells suspended at pH 8.5 and 300 mM external K+ failed to acidify their cytosol. The key observation indicative of the involvement of K+ transport in cytosolic acidification was that valinomycin (0.8 microM), a K+ uniporter, inhibited the growth of M. taylorii only at alkaline pH values. Experiments with resting cells indicated that at alkaline pH values valinomycin uncoupled catabolic reactions from ATP synthesis. Thus, K+/H+ antiport activity was proposed to account for the K+ extrusion and the uncoupling effect of valinomycin at alkaline pH values. Such antiport activity was demonstrated by the sharp drop in pH of the bulk medium of the cell suspension upon the addition of 0.1 M KCl. The antiporter appeared to be active only at alkaline pH values, which was in accordance with a possible role in pH homeostasis by M. taylorii growing at alkaline pH values.

Alkalies↗

PubMed1999

Regulation of expression of the fructan hydrolase gene of Streptococcus mutans GS-5 by induction and carbon catabolite repression.

The polymers of fructose, levan and inulin, as well as sucrose and raffinose, are substrates for the product of the fruA gene of Streptococcus mutans GS-5. The purpose of this study was to characterize the DNA immediately flanking fruA, to explore the regulation of expression of fruA by the carbohydrate source, and to begin to elucidate the molecular basis for differential expression of the gene. Located 3' to fruA was an open reading frame (ORF) with similarity to beta-fructosidases which was cotranscribed with fruA. A transcriptional initiation site, located an appropriate distance from an extended -10-like promoter, was mapped at 165 bp 5' to the fruA structural gene. By the use of computer algorithms, two overlapping, stable stem-loop sequences with the potential to function as rho-independent terminators were found in the 5' untranslated region. Catabolite response elements (CREs), which have been shown to govern carbon catabolite repression (CCR) by functioning as negative cis elements in gram-positive bacteria, were located close to the promoter. The levels of production of fruA mRNA and FruA were elevated in cells growing on levan, inulin, or sucrose as the sole carbohydrate source, and repression was observed when cells were grown on readily metabolizable hexoses. Deletion derivatives containing fusions of fruA promoter regions, lacking sequences 5' or 3' to the promoter, and a promoterless chloramphenicol acetyltransferase gene were used (i) to demonstrate the functionality of the promoter mapped by primer extension, (ii) to demonstrate that CCR of the fru operon requires the CRE that is located 3' to the promoter region, and (iii) to provide preliminary evidence that supports the involvement of an antitermination mechanism in fruA induction.

Amino Acid Sequence↗

PubMed1991

A mutation in the putative Mg(2+)-binding site of Gs alpha prevents its activation by receptors.

The properties of a Gs alpha mutant with an Asn substituted for Ser at position 54, designated mutant 54Asn alpha s, were studied after expression in S49 alpha s-deficient (cyc-) cells. Ser-54 in alpha s is comparable to Ser-17 in Ras, which is involved in binding Mg2+ associated with bound nucleotide. 54Asn alpha s did not restore either hormone-induced cyclic AMP production in intact cyc- cells or hormone-induced adenylyl cyclase activation in membranes isolated from these cells. The defect was a failure of ligand-bound receptor to activate 54Asn alpha s, since the mutant protein retained the ability to activate adenylyl cyclase in isolated membranes in the presence of GTP or GTP gamma S. Guanine nucleotide regulation of mutant alpha s suggested that it has increased guanine nucleotide exchange rates and an increased preference for diphosphates over triphosphates. Hormone stimulation magnified the preference of 54Asn alpha s for diphosphates, which could account for its inability to be activated by receptor. The properties of this mutant are discussed in terms of similarities to and differences with the analogous RasH mutant, which has been shown to interfere with endogenous Ras function in cells.

Adenylyl Cyclases↗

PubMed1995

Weak acid effects and fluoride inhibition of glycolysis by Streptococcus mutans GS-5.

Fluoride and a variety of other weak acids acted to reduce reversibily the acid tolerance of glycolysis by intact cells of Streptococcus mutans GS-5 as shown by higher final pH values in acid-drop experiments with glucose in excess. The order of effectiveness was fluoride > indomethacin > ibuprofen > ketoprofen > salicylate > sorbate > cinnamate > p-hydroxybenzoate > benzoate > ascorbate. Only fluoride also acted as an inhibitor of the glycolytic enzyme enolase. However, enolase in permeabilized cells was also inhibited by acidification with a sharp drop-off in activity between pH 6 and 5. It was proposed that the weak acids, including fluoride, acted to reduce glycolytic acid tolerance by enhancing cytoplasmic acidification and thereby inhibiting enzymes such as enolase. The potencies of the acids could not be predicted accurately from knowledge of pKa values, octanol-water partition coefficients, and molecular weights. It was concluded that their modes of action in acid sensitization involved perturbations of membrane function in addition to their acting as transmembrane carriers of protons. Methylparaben (methyl ester of p-hydroxybenzoate) was also a sensitizer but was less effective than the parent acid.

Acids↗

PubMed1998

FROM VACUOLAR GS-X PUMPS TO MULTISPECIFIC ABC TRANSPORTERS.

While the concept of H+-coupling has dominated studies of energy-dependent organic solute transport in plants for over two decades, recent studies have demonstrated the existence of a group of organic solute transporters, belonging to the ATP-binding cassette (ABC) superfamily, that are directly energized by MgATP rather than by a transmembrane H+-electrochemical potential difference. Originally identified in microbial and animal cells, the ABC superfamily is one of the largest and most widespread protein families known. Competent in the transport of a broad range of substances including sugars, peptides, alkaloids, inorganic anions, and lipids, all ABC transporters are constituted of one or two copies each of an integral membrane sector and cytosolically oriented ATP-binding domain. To date, two major subclasses, the multidrug resistance-associated proteins (MRPs) and multidrug resistance proteins (MDRs) (so named because of the phenotypes conferred by their animal prototypes), have been identified molecularly in plants. However, only the MRPs have been defined functionally. This review therefore focuses on the functional capabilities, energetics, organization, and regulation of the plant MRPs. Otherwise known as GS-X pumps, or glutathione-conjugate or multispecific organic anion Mg2+-ATPases, the MRPs are considered to participate in the transport of exogenous and endogenous amphipathic anions and glutathionated compounds from the cytosol into the vacuole. Encoded by a multigene family and possessing a unique domain organization, the types of processes that likely converge and depend on plant MRPs include herbicide detoxification, cell pigmentation, the alleviation of oxidative damage, and the storage of antimicrobial compounds. Additional functional capabilities might include channel regulation or activity, and/or the transport of heavy metal chelates. The identification of the MRPs, in particular, and the demonstration of a central role for ABC transporters, in general, in plant function not only provide fresh insights into the molecular basis of energy-dependent solute transport but also offer the prospect for manipulating and investigating many fundamental processes that have hitherto evaded analysis at the transport level.

Journal Article↗

PubMed1992

Gs and Gi protein subunits during cell differentiation in intestinal crypt-villus axis: regulation at the mRNA level.

The expression of subunits of the guanine nucleotide regulatory protein that mediates hormonal stimulation of adenylyl cyclase (Gs) and of the guanine nucleotide regulatory protein that mediates hormonal inhibition of adenylyl cyclase (Gi) was studied during cell migration and differentiation in the rat small intestine crypt-villus axis. Proliferative crypt cells were separated from nonproliferative mature villus cells and the following data were obtained: 1) alpha s subunits were more abundant in crypt cells than in villus cells as evidenced by cholera toxin-catalyzed [32P]NAD ribosylation and Western blotting of this relative molecular weight (M(r)) 42,000 protein; 2) alpha i2- and alpha i3-subunits (M(r) 40,000 and M(r) 41,000, respectively) were preferentially expressed in villus cells as evidenced by pertussis toxin-catalyzed [32P]NAD ribosylation and Western blotting (alpha i1-subunit was not detectable in intestinal epithelium by using these techniques); 3) Western blotting showed a higher expression of the common beta- (M(r) 36,000) subunit of G proteins in villus cells than in crypt cells; and 4) Northern blot analysis using an alpha s-subunit oligonucleotide probe showed a 1.9-kb mRNA that was more abundant in crypt cells than in villus cells. In contrast, alpha i2- and alpha i3-mRNA species (2.3 and 3.5 kb, respectively), analyzed by using specific cDNA probes, were much more abundant in villus cells than in crypt cells. Finally, two beta-subunit mRNA species of 3.3 and 1.8 kb were detectable in intestinal epithelial cells and were more abundant in villus cells than in crypt cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate Ribose↗

PubMed1988

Alpha-subunit of Gs directly activates cardiac calcium channels in lipid bilayers.

Specific guanine nucleotide-binding proteins (G proteins) couple receptors to calcium channels indirectly via cytoplasmic agents such as protein kinases (Birnbaumer et al., Kidney Int. 32: 514-537, 1987). Direct coupling between the stimulatory G protein from adenylyl cyclase (Gs) and calcium channels has been shown recently in inside-out cell-free membrane patches excised from guinea pig myocytes, i.e., in the absence of cytoplasm (Yatani et al., Science Wash. DC 238: 1288-1292, 1987). In these patches, single calcium channel currents were unstable, and this complicated both the experiments and their interpretation. Calcium currents are more stable when calcium channels are incorporated into planar lipid bilayers (Rosenberg et al., Science Wash. DC 231: 1564-1566, 1986), and consequently, we used the latter method to examine the direct coupling hypothesis more fully. Bovine cardiac sarcolemmal vesicles were added to the cis side of a chamber divided by a preformed planar lipid bilayer. The cytoplasmic surface faced the trans chamber and was bathed by an ATP-free minimal solution. The extracellular solution in the cis chamber contained 100 mM Ba2+, and both chambers contained the dihydropyridine agonist BAY K 8644 at 1 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylate Cyclase Toxin↗

PubMed1997

Inhibitory effects of Gs on desensitization of beta-adrenergic receptors in tracheal smooth muscle.

We examined the reduction of mechanical responsiveness to beta-agonists after continuous or repeated exposure to agonists in guinea pig tracheal smooth muscle, using an isometric tension record. The inhibitory action of 0.1 microM isoproterenol (Iso) on contraction induced by 1 microM methacholine (MCh) was suppressed markedly after incubation with 0.0003-3 microM Iso for 1 h. The effects of Iso on MCh-induced contraction gradually decreased after repeated application of these agents at intervals of 1 h. When Iso was perfused cumulatively to tissues repeatedly precontracted by MCh, the effects of Iso were reduced at the second application. This reduced responsiveness to beta-agonists was not mimicked by forskolin and did not occur after preexposure of the strips to 2 micrograms/ml cholera toxin for 6 h. We concluded that this reduced responsiveness to beta-agonists is homologous desensitization and that the irreversible activation of the stimulatory G proteins, Gs, may play an important role in prevention of the reduced responsiveness to beta-agonists.

Adrenergic beta-Agonists↗

PubMed1989

Interactions of zinc with fluoride on growth, glycolysis and survival of Streptococcus mutans GS-5.

Effects of zinc and/or fluoride on growth, glycolysis and survival of Streptococcus mutans GS-5 were examined in vitro. Zinc inhibited growth and glycolysis, and enhanced the antimetabolic activity of fluoride. Zinc alone had little effect on cell survival. During cell growth without pH control a protection from cell death was mediated by fluoride, which appeared to be caused by a higher final pH in the culture medium. When cell death was observed under controlled pH conditions in a lactate-acetate buffer at pH 6.5, 5.0 or 4.0, fluoride was bactericidal only at pH 4.0. However, the combination of zinc plus fluoride was strongly bactericidal at all pH values that were tested.

Acids↗

PubMed1990

Interactions of selenium and fluoride on growth, glycolysis and survival of Streptococcus mutans GS-5.

The effects of low concentrations (1.0 mmol/l of selenite and seleno-dl-cystine were tested alone, or in combination with NaF, on growth, glycolysis, and survival of Streptococcus mutans GS-5. In batch culture, both selenium-containing compounds (1.0 mmol/l) inhibited the growth rate and final cell yield by 92% or greater; glycolysis, however, was not affected. The observed bactericidal action of selenite at 0.1 mmol/l was pH-dependent. Fluoride reduced the killing effect of SeO3 in the culture medium and in a lactate-acetate buffer system at pH 6.5, 5.0 and 4.0. These data indicate that selenium-containing compounds exert an antibacterial action on cells of S. mutans in a manner which leaves glycolysis unaffected.

Animals↗

PubMed1995

Interaction of chlorhexidine with cytoplasmic membranes of Streptococcus mutans GS-5.

Cytoplasmic membranes of Streptococcus mutans GS-5 were extracted by incubating cells with 1% sodium lauroyl sarcosinate for 20 min at room temperature. The profiles of membrane proteins were determined by SDS-PAGE and isoelectric focusing. The effect of chlorhexidine digluconate on cell membranes was studied after treating the extracted proteins for 30 min with the drug at final concentrations of 0.05 and 0.2%. Chlorhexidine caused selective reduction in the intensity of the membrane proteins. Five densely staining bands with molecular weights of 24.2, 19.6, 18.1, 17.6 and 16.4 kD were obviously diminished. Isoelectric focusing indicated that chlorhexidine preferably precipitated acidic cytoplasmic proteins (pI 4.0-4.92). Our results are consistent with the hypothesis that the mode of action of this drug is mainly attributed to its hydrophilic property. Chlorhexidine, being cationic, may interact with bacteria by attraction to negative-charge membrane components.

Adenosine Triphosphatases↗

PubMed1994

Cloning of the alpha-subunit of GS protein from spontaneously hypertensive rats.

Enhanced sodium reabsorption by the kidney has a significant role in the development of genetic hypertension. In the spontaneously hypertensive rat (SHR) model of genetic hypertension, the enhanced sodium reabsorption likely arises from abnormal hormonal regulation of tubular transport. Since hormonal signaling pathways are coupled frequently via GTP binding proteins, one explanation for hormonal abnormalities in SHR would be a defect in a GTP binding protein or proteins. Recent work has suggested that the regulation of Na+,K(+)-ATPase activity by cholera toxin-sensitive GTP binding proteins is abnormal in SHR. The purpose of the present studies was to clone the alpha S-subunit, which is the subunit ADP ribosylated by cholera toxin, of GS protein to determine whether it is abnormal in SHR. Reverse transcription-polymerase chain reaction was able to detect mRNA for alpha S in both Wistar-Kyoto (WKY) rats and SHR. Northern analysis indicated that equivalent amounts of alpha S mRNA were present in WKY rats and SHR. S1 nuclease analysis demonstrated that there was no difference in the amount of alpha S short and long forms between WKY rats and SHR. Subcloning and sequencing of polymerase chain reaction products from WKY rats and SHR indicated that the alpha S forms present in renal cortex were identical. ADP ribosylation studies with cholera toxin demonstrated the presence of equivalent amounts of alpha S protein in WKY rats and SHR. Taken together, these results suggest that the abnormal regulation of Na+,K(+)-ATPase activity by a cholera toxin-sensitive pathway in SHR does not arise from a defect in the alpha S subunit.

Adenosine Diphosphate Ribose↗

PubMed1996

Adverse effects of chronic endogenous sympathetic drive induced by cardiac GS alpha overexpression.

To study the physiological effect of the overexpression of myocardial Gsalpha (protein levels increased by approximately threefold in transgenic mice), we examined the responsiveness to sympathomimetic amines by echocardiography (9 MHz) in five transgenic mice and five control mice (both 10.3 +/- 0.2 months old). Myocardial contractility in transgenic mice, as assessed by left ventricular (LV) fractional shortening (LVFS) and LV ejection fraction (LVEF) was not different from that of control mice at baseline (LVFS, 40 +/- 3% versus 36 +/- 2%; LVEF, 78 +/- 3% versus 74 +/- 3%). LVFS and LVEF values in transgenic mice during isoproterenol (ISO, 0.02 micrograms/kg per minute) infusion were higher than the values in control mice (LVFS, 68 +/- 4% versus 48 +/- 3%; LVEF, 96 +/- 1% versus 86 +/- 3%; P < .05). Norepinephrine (NE, 0.2 micrograms/kg per minute) infusion also increased LVFS and LVEF in transgenic mice more than in control mice (LVFS, 59 +/- 4% versus 47 +/- 3%; LVEF, 93 +/- 2% versus 85 +/- 3%; P < .05). Heart rates of transgenic mice were higher than those of control mice during ISO and NE infusion. In three transgenic mice with heart rates held constant, LV dP/dt rose by 33 +/- 2% with ISO (0.02 micrograms/kg per minute) and by only 13 +/- 2% in three wild-type control mice (P < .01). NE (0.1 micrograms/kg per minute) also induced a greater effect on LV dP/dt in the three transgenic mice with heart rates held constant compared with three wild-type control mice (65 +/ 8% versus 28 +/- 4%, P < .05). Pathological and histological analyses of older transgenic mouse hearts (16.0 +/- 0.8 months old) revealed hypertrophy, degeneration, atrophy of cells, and replacement fibrosis reflected by significant increases in collagen volume in the subendocardium (5.2 +/- 1.4% versus 1.2 +/- 0.3%, P < .05) and in the cross-sectional area of myocytes (298 +/- 29 versus 187 +/- 12 micron2, P < .05) compared with control mouse hearts. These results suggest that Gsalpha overexpression enhances the efficacy of the beta-adrenergic receptor-Gs-adenylyl cyclase signaling pathway. This in turn leads to augmented inotropic and chronotropic responses to endogenous sympathetic stimulation. This action over the life of the animal results in myocardial damage characterized by cellular degeneration, necrosis, and replacement fibrosis, with the remaining cells undergoing compensatory hypertrophy. As a model, this transgenic mouse offers new insights into the mechanisms of cardiomyopathy and heart failure and provides a new tool for their study.

Animals↗

PubMed1983

Acid sensitivity of glycolysis in normal and proton-permeable cells of Streptococcus mutans GS-5.

Gramicidin, an ionophoric antibiotic which enhances proton permeability of cell membranes, was found to increase the acid sensitivity of glycolysis by intact cells of Streptococcus mutans GS-5, to inhibit uptake of 2-deoxyglucose at pH values of 5.5 or less, and to cause a decrease in the intracellular levels of early intermediates of glycolysis. The inhibitory effects of the antibiotic on glycolysis at low pH values were related to inhibition of sugar uptake via the phosphotransferase system.

Acids↗

PubMed1986

Dexamethasone effects on beta-adrenergic receptors and adenylate cyclase regulatory proteins Gs and Gi in ROS 17/2.8 cells.

Treatment of ROS 17/2.8 cells with dexamethasone (dex) increases (-)isoproterenol (ISO)-, PTH-, cholera toxin-, guanine nucleotide-, NaF-, and forskolin-stimulated adenylate cyclase activity. Enhanced hormone stimulation was first apparent 12 h after dex addition. (-)-[3H]Dihydroalprenolol binding, displaceable by ISO, increased up to 2-fold in dex-treated cells. This effect depended on protein synthesis and closely paralleled the extent and time course of the increase in adenylate cyclase stimulation. In dex-treated cells there was also an increase in the maximum velocity of guanyl-5'-yl imidodiphosphate-stimulated adenylate cyclase, a decrease in the lag time for guanyl-5'-yl imidodiphosphate enzyme activation in the presence of ISO from 3 to 1 min, increased stimulation of adenylate cyclase by cholera toxin, and increased labeling of 47,000 and 42,000 mol wt proteins by [32P]NAD in the presence of cholera toxin. [32P]NAD ribosylation in the presence of pertussis toxin resulted in the labeling of 40,000 mol wt protein, which was also increased by 20-50% in dex-treated cells. However, pertussis toxin treatment did not augment or reduce the effect on hormone stimulation, although it increased the cAMP response to PTH and (-)ISO. These findings suggest that dex increases (-)ISO stimulation of adenylate cyclase in ROS 17/2.8 cells by jointly increasing the number of hormone receptors and the abundance of Gs, the guanine nucleotide binding regulatory protein.

Adenosine Diphosphate Ribose↗

PubMed1987

Dexamethasone increases adenylyl cyclase activity and expression of the alpha-subunit of Gs in GH3 cells.

Glucocorticoids regulate responsiveness of many different cells and tissues to hormones that act by stimulating adenylyl cyclase. In a rat pituitary cell line, GH3, exposure to dexamethasone (150 mM for 72 h) doubled the specific activity of adenylyl cyclase in membrane extracts, whether the enzyme was stimulated by guanine nucleotides, vasoactive intestinal peptide, or forskolin. Dexamethasone treatment of GH3 cells also caused a 5-fold increase in RNA encoding the alpha-chain of Gs (alpha s) as well as a 2-fold increase in membrane-bound alpha s-polypeptide, measured by either of two assays: 1) Biochemical complementation of the alpha s deficiency of S49 lymphoma cyc- membranes in vitro; 2) Cholera toxin-catalyzed ADP ribosylation of 45- and 52-kilodalton alpha s-polypeptides. These observations suggest that glucocorticoid-induced enhancement of adenylyl cyclase activity in GH3 cells is mediated, at least in part, by increased expression of alpha s.

Adenylyl Cyclases↗

PubMed1989

Neural control of the alpha-subunit of Gs messenger ribonucleic acid in rat brown adipose tissue.

Neural stimulation of rat interscapular brown adipose tissue (IBAT) can greatly modify transmembrane signalling in this tissue. As part of an investigation into the molecular mechanisms of such modulation we have examined the effects of surgical denervation of BAT and cold exposure (a treatment that increases neural stimulation of BAT) on the levels of mRNA encoding for the alpha-subunit of Gs, the GTP-binding protein that regulates adenylate cyclase. The G alpha s mRNA content of BAT per unit RNA was 5-10 times greater than that of lung, liver, or caudate-putamen. Surgical denervation of BAT of warm-adapted rats reduced G alpha s mRNA content by 30% within 8 h postsurgery and by 65% by 72 h. Concurrent infusion of norepinephrine completely prevented the denervation-induced decline in G alpha s mRNA at 72 h. Infusion of the beta-adrenergic agonist isoproterenol also prevented the denervation-induced decline in G alpha s mRNA, but infusion of the alpha 1-adrenergic agonist phenylephrine was without effect. Exposing rats to 4 C for 3 days approximately doubled the level of G alpha s mRNA. Interestingly, surgical denervation did not prevent the cold-induced increase in G alpha s mRNA levels, indicating that this effect is independent of local innervation. Despite reducing G alpha s mRNA levels by about 60%, surgical denervation failed to alter the concentration of G alpha s protein in IBAT membranes of warm-adapted rats, as determined by immunoblotting. Previous work indicates that cold exposure does not increase the concentration of G alpha s in IBAT membranes. Taken with the present results, these data indicate that there is no simple relationship between tissue G alpha s mRNA content and membrane G alpha s concentration in IBAT.

Acclimatization↗