Changed sensitivity to antigen in a gut epithelium treated with bile salts

Colonic epithelia from guinea-pigs, sensitized by feeding with cow milk, responded to antigen (beta-lactoglobulin) challenge when applied to the serosal, but not the mucosal, side of the tissue. The response, under short circuit conditions, was an inwardly directed current due to chloride secretion. Two detergents, deoxycholate and Triton X-100, caused the basal short circuit current to decrease and transepithelial conductance to increase when applied to the mucosal surface. After removing detergents from the bathing solution tissues now responded to antigen challenge from the mucosal side, without impairment of the overall response. There was a correlation between the conductance change induced by detergents and the fraction of the total response which could be elicited form the mucosal side of the tissue. It was concluded that models of local hypersensitivity reactions to ingested foodstuffs require both development of immunological sensitivity plus increased permeability to antigen. The role of bile salts in inducing the latter is discussed.

Characterization of extracellular phospholipase A2 in rheumatoid synovial fluid

Phospholipase A2 (PLA2) activity has now been identified in rheumatoid synovial fluids. This PLA2 is a calcium-requiring protein of MW 11,000 with a neutral pH optimum. Its activity was inhibited by high concentrations of Mg2+, and by the active site-directed histidine reagent p-bromophenacyl bromide. Ionic and nonionic detergents, or the sulfhydryl reagent dithiothreitol caused loss of enzyme activity. Synovial fluid PLA2 did not interact with sulphated mucopolysaccharides such as heparin or chondroitin sulphate. Release and sequestration of PLA2 in the joint space may contribute to the characteristic rheumatoid inflammatory changes.

Behaviour of cardiac microsomal Ca2+ pump under conditions that may simulate pathological situations

The behaviour of Ca2+ ATPase activity in relation to Ca2+ transport process was studied under different experimental conditions in canine cardiac microsomal fraction predominantly containing sarcoplasmic reticulum. The total Ca2+ concentration required for half maximal activation (Ka) of microsomal Ca2+ ATPase and Ca2+ uptake did not differ significantly, unless 0.1 mmol/l EGTA was present in the incubation media. Pretreatment of cardiac microsomes with membrane disruptive agents like phospholipase A, trypsin as well as deoxycholate strongly increased (2-3 fold) Ca2+ ATPase activity but uptake rate of Ca2+ declined. Only in phospholipase C and beta-glucuronidase pretreatment, a parallel decrease of Ca2+ ATPase and uptake was observed. In presence of excess (free)Ca2+ (greater than 10 mumol/l) both Ca2+ ATPase as well as Ca2+ uptake were inhibited, however, Ca2+ binding process remained unaltered. Likewise, low pH completely altered the relation between Ca2+ binding and ATPase activity; whereas Ca2+ ATPase was inhibited, Ca2+ binding did not change. Our present data provide evidence for some cellular factors that may be involved in producing uncoupling of microsomal Ca2+ ATPase from Ca2+ accumulation process that was previously observed in various pathological situations.

Mechanisms underlying the intestinal fluid secretion evoked by nociceptive serosal stimulation of the rat

Intestinal net fluid transport was measured in vivo continuously with a gravimetric method. Chemical stimulation of the jejunal serosa with hydrochloric acid (0.1 M), ethanol (20%), cat bile or 7-deoxycholic acid (10 mM) evoked an intestinal fluid secretion. Hexamethonium (10 mg/kg b.wt.i.v.) or serosal application of lidocaine (1% solution) partially blocked this secretory response. Bradykinin and prostaglandin E1, two important inflammatory mediators, elicited fluid secretion when applied to the serosal surface at a concentration of 10(-4) M. This secretion was also partly inhibited by hexamethonium. Furthermore indomethacin (10 mg/kg b.wt. i.v.) or pyrilamine (10 mg/kg b.wt. i.v.), a H1-receptor blocker, partly inhibited the secretory response caused by chemical stimulation of the serosa while cimetidine (1 mg/kg b.wt. i.v.), a H2-receptor blocker, had no effect. Freeze sectioned samples from chemically stimulated intestines were examined by fluorescence microscopy. A leakage of i.v. administrated Evans blue labelled albumin into the interstitial space of the serosa and the outer layer of the muscularis was found. It is concluded: The intestinal fluid secretion studied is mainly elicited by nociceptive stimulation of nerves in the serosa or the outer muscularis. The reflex may be activated by the local release of histamine, kinins and prostaglandins. The reflex studied is part of an inflammatory response.

Effects of the virulence plasmid ColV, I-K94 on the sensitivity of Escherichia coli to putative environmental inhibitory agents

Derivatives of Escherichia coli carrying the virulence plasmid, ColV, I-K94 were more resistant than the ColV- parents to phage Mel but were more sensitive to the hydrophobic inhibitors deoxycholate, erythromycin and lysozyme. The basis for these changes in sensitivity has been examined in ColV+ mutants with altered colicin or VmpA protein levels and in ColV+ strains with repressed transfer properties.

Solubilization of human sperm antigens

Various methods of solubilization of human sperm antigens were compared by testing the sperm extracts against rabbit antihuman spermatozoa immune serums with double immunodiffusion and rocket immunoelectrophoresis. Marked differences were found in the protein contents and the SDS-PAGE protein patterns of the extracts. Lithium diiodosalicylate was the most efficient in solubilizing the sperm proteins and in preserving their antigenicity. Nonionic detergents also gave, either alone or combined to sonification and 1.0 M KCl, 24-28 clearly discernible protein bands and several different immunoprecipitates. Ionic detergents deoxycholate and cetylpyridinium chloride solubilized a high yield of proteins, but their antigenity was poor.

Properties of rat liver signal peptidase reconstituted into liposomes

EDTA/KCl- or pyrophosphate-treated rough microsomes of rat liver clearly showed the co-translational cleavage of pre-human placental lactogen and translocation of the product into membrane vesicles. The signal peptidase fraction was isolated by chromatography on Sephacryl S-300 of deoxycholate-treated membranes and reconstituted into liposomes by dialysis or by the Biobeads SM-2 method. Assay of the signal peptidase activity was performed with pre-human placental lactogen synthesized by the reticulocyte lysate system programmed with human placental lactogen mRNA. The signal peptidase reconstituted into liposomes showed stable activity over the temperature range of 0 to 45 degrees C; in contrast, the detergent-solubilized signal peptidase of dog pancreatic membranes was completely inactivated at the unusually low temperature of 37 degrees C. It was shown that this inactivation was due to the presence of detergent. Signal peptidase from rat liver was insensitive to a variety of protease inhibitors, like the enzyme from dog pancreas, but differed from the latter in being inhibited by chymostatin and TPCK.

Composition of renal basement membranes isolated under various conditions

GBM isolated from a surgical biopsy directly or after a 22 hr incubation period--to imitate the usual interval between death and isolation--appeared to be nearly identical in amino acid composition. Sonication and detergent procedures for isolation of GBM and TBM lead to preparations of different chemical composition. Phosphorus analysis and electron micrographs indicate the presence of material of supposedly cellular origin in sonicated but not in detergent-treated bovine and human GBM. Detergent-treated bovine and human GBM preparations are more enriched in the collagen-typical amino acids than sonicated samples. SDS-PAGE analyses show a nearly identical polypeptide pattern. Sonicated and detergent-treated bovine TBM preparations are free of cellular material. They show in SDS-PAGE a similar heterogeneous polypeptide pattern, but with lower intensities of three components with molecular weights between 30 and 60 kdalton. Sulfated GAG's are present in higher concentration in sonicated than in detergent-treated GBM and TBM. Collagen is not extracted from glomeruli and tubules by detergent treatment.

Hyodeoxycholic acid: a new approach to gallstone prevention

Hyodeoxycholic acid and its isomer, 6 beta-hyodeoxycholic acid, when added to a lithogenic diet prevented the formation of cholesterol gallstones and crystals in prairie dogs. This beneficial effect occurred in the presence of bile supersaturated with cholesterol. Hyodeoxycholic acid abolished the feedback inhibition of hepatic hydroxymethylglutaryl coenzyme A reductase activity, the rate-limiting enzyme of cholesterol synthesis, and prevented elevations in serum and liver cholesterol observed in animals fed a 0.4 percent cholesterol diet. The gallbladder bile of the animals fed hyodeoxycholic acid and 6 beta-hyodeoxycholic acid contained abundant liquid crystals. This suggests that these bile acids prevented the transition of cholesterol from its liquid crystalline phase to solid crystals and stones.

Effect of deoxycholic acid on the tumour incidence, distribution, and receptor status of colorectal cancer in the rat model

It has previously been observed that 25% of human colorectal cancers contain specific receptors to deoxycholic acid (DCA). In the present study, the effect of intrarectal instillation of DCA on tumour number, distribution, size, and DCA receptor status was measured in rats receiving the colorectal carcinogen, azoxymethane. Rats treated with azoxymethane and intrarectal DCA developed significantly more colorectal cancers than rats receiving azoxymethane and intrarectal saline (median 11.5, range 8-17 vs. median 6.0, range 3-9 tumours/rat, respectively, p less than 0.01). This reflected a significantly higher number of tumours in the distal colon of the DCA-treated group (median 8.0, range 5-10 tumours/rat) compared to the saline-treated group (p less than 0.01). In those rats receiving DCA and azoxymethane, 5 of 12 tumours tested were found to be DCA receptor-positive, compared with only 1 of 11 in the saline and azoxymethane group. These results confirm the belief that DCA acts as a tumour promoter, and suggest a possible role for DCA receptors.

Regulation of lipoprotein lipase in primary cultures of isolated human adipocytes

To study the regulation of adipose tissue lipoprotein lipase (LPL) in human adipocytes, omental adipose tissue was obtained from healthy subjects and digested in collagenase. The isolated adipocytes thus obtained were suspended in Medium 199 and cultured at 37 degrees C. Cell viability was demonstrated in adipocytes cultured for up to 72 h by constancy of cell number, cell size, trypan-blue exclusion, and specific 125I-insulin binding. In addition, chloroquine induced an increase in cell-associated 125I-insulin at 24, 48, and 72 h after preparation. Thus, isolated adipocytes retained their ability to bind, internalize, and degrade insulin. LPL was measured as activity secreted into the culture medium (CM), released from cells by heparin (HR), and extracted from cell digests. A broad range of heparin concentrations produced a prompt release of LPL from a rapidly replenishable pool of cellular activity. When cells were cultured in medium containing 10% fetal bovine serum, there was a marked stimulation of CM and HR. The secretory response to serum (CM) correlated strongly with HR 24 h after preparation (rs = 0.731, P less than 0.001). In addition, HR was found to correlate logarithmically and inversely with body mass index (r = -0.731, P less than 0.001). Insulin, at 400 ng/ml only, increased HR by 36 +/- 10%, an effect simulated by lower concentrations of insulin-like growth factor-1 (IGF1). Thus, LPL is produced and regulated in isolated human adipocytes. The degree of adiposity and serum are important regulators of HR activity, whereas insulin is stimulatory only at a pharmacologic concentration. This effect of insulin may be mediated through the IGF1 receptor. Isolated human adipocytes represent a novel and useful system for the study of LPL and lipid metabolism as well as for other aspects of adipocyte biology.

Decline in infectivity of simian virus 40 by sodium deoxycholate and its restoration with the extract of monkey kidney cells

Plaque-forming activity and T-antigen-synthesizing activity in the crude preparation of simian virus 40 (SV40) decreased to 1/20-27 after treatment with 0.5% sodium deoxycholate (DOC) for 30 min at 37 degrees C. A full restoration of the activity occurred after incubation of DOC-treated virions with the extract of monkey CV-1 cells, host cells for productive infection with SV40. Analysis by sedimentation through 15% sucrose to CsCl cushion (rho = 1.327 g/cm3) revealed that virions in the [35S]methionine-labeled crude virus preparation sedimented to the interface between CsCl and sucrose, and that treatment with DOC resulted in the loss of infectivity and the appearance of virions sedimentable into CsCl cushion. The [35S]methionine-labeled purified virions (prepared after treatment with DOC and sedimentable into CsCl cushion) sedimented to the CsCl-sucrose interface after incubation with the cell extract, with restoration of infectivity. The infectivity-restoring activity of the cell extract was sensitive to ethyl ether, partially sensitive to heating at 75 degrees-97 degrees for 30 min, but resistant to treatment with DNase (50 micrograms/ml), RNase (40 micrograms/ml), or trypsin (0.05%) for 30 min at 37 degrees. These results suggest that lipid-related cellular components bind stably to virions of SV40 and facilitate an efficient infection.

Inhibitory effect of unconjugated bile acids on the intestinal transport of 5-methyltetrahydrofolate in rat jejunum in vitro

The effect of the unconjugated bile acids, cholic, deoxycholic, chenodeoxycholic, and ursodeoxycholic acids, and of the conjugated bile acid taurocholic acid on the mucosal-to-serosal transport and tissue uptake of the naturally occurring folate derivative, 5-methyltetrahydrofolate (5-CH3H4PteGlu) was examined in everted sacs of rat jejunum. Each of the unconjugated bile acids examined inhibited the transport and tissue uptake of 5-CH3H4PteGlu in a concentration dependent manner. At low concentrations (0.01-0.1 mM) of cholic and deoxycholic acids, no structural or functional damage to the intestinal mucosa occurred and the transport of 5-CH3H4PteGlu was inhibited competitively with Ki values of 0.114 mM and 0.055 mM for cholic and deoxycholic acids, respectively. The greater inhibition of 5-CH3H4PteGlu transport by unconjugated bile acids at 1 mM can be attributed to observed structural and functional damage to the intestinal mucosa. The addition of 2 mM lecithin to the mucosal medium failed to prevent the inhibitory effect of 0.1 mM deoxycholic acid on the transport of 0.5 microM 5-CH3H4PteGlu. Compared with the effect of unconjugated bile acids, the conjugated bile acid taurocholic acid (0.01-5 mM) showed no effect on the transport and tissue uptake of 5-CH3H4PteGlu. The results of this study show that intestinal transport and tissue uptake of 5-CH3H4PteGlu are inhibited by unconjugated bile acids in a dose-dependent fashion. The clinical and physiological implications of these observations are discussed.

The effects of detergents on CDP-choline:1,2-diacylglycerol phosphocholine transferase from hamster heart

The effects of detergents on CDP-choline:1,2-diacylglycerol phosphocholine transferase from hamster heart were examined. Maximum enhancement of enzyme activity was produced by Tween-20, while Triton X-100 caused a small increase in enzyme activity. No enhancement of enzyme activity was observed with deoxycholate or ethanol. Although enzyme activity was enhanced by different concentrations of Tween-20 (15-120 micrograms/mL), a substantially higher concentration of diacylglycerol was required when the concentration of Tween-20 in the assay was greater than 30 micrograms/mL. In the presence of Tween-20, a sigmoidal curve was obtained when enzyme activity was plotted versus diacylglycerol concentrations. The sigmoidal curve became more prominent when a higher amount of Tween-20 was used. It appears that the enhancement of enzyme activity by Tween-20 was not caused by the direct action of the detergent on the enzyme, but probably resulted in a better dispersion of the lipodal substrate which facilitates better utilization by the enzyme. The acyl specificity of the enzyme in the presence of detergent was found to be rather limited and the highest enzyme activity was obtained with diacylglycerols containing a monounsaturated acyl group at the C-2 position.

Attempts to establish the scrapie agent in cell lines

Attempts were made to establish a persistent infection with scrapie agent in four murine cell lines. Of the four lines tested, viz. P388D1, P3-NS1-Ag-1 (NS1), L cells and an NS1 spleen cell hybrid, only the NS1 cell line showed any evidence of agent replication. Ten per cent dimethylsulphoxide (DMSO) was included in the culture media of L cells inoculated with scrapie agent. This treatment raised the initial levels of scrapie agent associating with the L cells but did not result in a persistently infected cell line. An effect of DMSO in the inoculum was observed in mice inoculated intraperitoneally, the incubation period of the disease was considerably shortened.

Influence of serosal hydrostatic pressure on net water and electrolyte transport across the isolated rat colonic mucosa exposed to different secretagogues

The influence of 2 cm and 7 cm hydrostatic pressure applied upon the serosal side on net water and electrolyte transport and paracellular permeability was investigated in everted sacs of stripped rat colon mucosa exposed to different secretagogues. A 2 cm pressure abolished net fluid absorption in the presence of deoxycholic acid, bisacodyl, ethacrynic acid and rhein and reduced absorption in the tissue pretreated with cholera toxin. The paracellular permeability was increased by deoxycholic acid, bisacodyl and ethacrynic acid and diminished under the influence of rhein and cholera toxin. At a pressure of 7 cm H2O fluid movement was directed toward the mucosal side parallel to the increase of the paracellular permeability. The fluid appearing at the mucosal side was isotonic in the presence of deoxycholic acid, ethacrynic acid and rhein but hypotonic when the tissue was pretreated with cholera toxin. From the pressure-induced net water flow and the composition of the transferred fluid secretagogues acting predominantly on paracellular pathway can be distinguished from secretagogues acting on basis of other mechanisms.

Absorption of 5-methyltetrahydrofolate in rat jejunum with intact blood and lymphatic vessels

Transport results from in vitro studies may not be applicable to in vivo situations. In this study, we extended our previous in vitro observations regarding the intestinal transport of 5-methyltetrahydrofolate to in vivo studies in the unanesthetized rat and examined the effect of the unstirred water layer on the absorption process. We used a well defined intestinal perfusion technique. Absorption of 0.5 and 5 microM 5-methyltetrahydrofolate proceeded in a linear manner for 40 min of perfusion at 0.31 and 1.74 nmol/100 cm per min, respectively. Absorption of 0.5 microM 5-methyltetrahydrofolate increased with increasing perfusate flow-rate from 0.5 to 2 to 4 ml/min, indicating an unstirred water layer influence on the absorption rate. Absorption of the substrate was saturable with an apparent Kt of 5.7 microM and Vmax of 3.45 nmol/100 cm per min. Absorption was pH-dependent, and was inhibited by structural analogues. In contrast to the in vitro data, addition of glucose (20 mM) to the perfusate was unnecessary for in vivo absorption to proceed. Unconjugated cholic (5 mM) and deoxycholic (1 mM) acids and the organic anion rose bengal (0.1 mM) inhibited the absorption of 0.5 microM 5-methyltetrahydrofolate when added to the perfusate.

CONCLUSIONS

the results of previous in vitro studies of 5-methyltetrahydrofolate intestinal transport are applicable to in vivo situations, except that luminal glucose was found to be unnecessary in the latter. The unstirred water layer modulated the absorption of 5-methyltetrahydrofolate, while unconjugated bile acids and rose bengal inhibited it.

Cytoplasmic location of linoleoyl-CoA desaturase in microsomal membranes of rat liver

The intramembrane localization of linoleoyl-CoA desaturase in rat liver microsomes was examined by various methods, such as digestion by proteases, effect of detergents, and inhibition by the antibodies against purified terminal desaturase. Exposure of the desaturase on the surface of microsomal vesicles was suggested by the fact that the enzyme activity in the intact microsomes was susceptible to tryptic digestion, and considerably inhibited by anti-desaturase antibodies. When microsomes were previously treated with trypsin, the enzyme became more susceptible to the antibodies. Furthermore, it was demonstrated that the protein fragments cleaved from microsomal membranes by tryptic digestion formed a single precipitin line with the antibodies by the double-immunodiffusion test. These findings suggest the presence of linoleoyl-CoA desaturase on the cytoplasmic surface in the endoplasmic reticulum, since tryptic digestion liberates only the protein components situated on the surface area of membranes. In addition, desaturase activity in the intact microsomes was not stimulated by addition of the detergent, indicating the further outside location of the active site of the enzyme in microsomal vesicles. The pretreatment of microsomes with a low concentration (0.05%) of sodium deoxycholate, which destroys the permeability barrier for macromolecules without membrane disassembly, did not increase the susceptibility to tryptic digestion and the antibodies. These results show that linoleoyl-CoA desaturase is not present in a latent state in the membrane.

Further studies on the properties of bile acids. I. Bile acid-induced changes of the action of drugs acting on the autonomic nervous system on the heart and blood vessels

The action of certain drugs on the autonomic system was studied under the influence of bile acids: 3,12-dihydroxycholanic acid (deoxycholic), 3,7,12-trihydroxycholanic acid (cholic), and 3,7,12-triketocholanic acid (dehydrocholic). The experiments were carried out on rat heart in vivo and on isolated rat vessel preparation. It was shown that bile acids reduced the stimulating effect of isoprenaline on rat heart and the relaxing effect on the blood vessels. An inversion of the effects of adrenaline and noradrenaline on the rat heart was observed, and an enhancement of the vasoconstrictor effect of these substances. Under the conditions of this experiment an inversion was noted of the action of acetylcholine on the heart and blood vessels.

Effect of albumin on the in vitro conjugation of bilirubin by rat liver microsomes

These studies were carried out to determine whether bovine serum albumin (BSA), which is usually included in the incubation mixture for the in vitro determination of bilirubin-UDP-glucuronyl transferase (GT) activity, affects GT activity. Using bilirubin as substrate, addition of BSA to the enzyme reaction mixture at concentrations varying from 2 to 30 mg/ml resulted in a dose-related inhibition of "native" GT activity of rat liver microsomes. When detergent-activated enzyme was employed, increasing concentrations of BSA also required higher concentrations of deoxycholate, digitonin, or Triton X-100 to produce maximal bilirubin conjugation. Low BSA concentrations (2 mg/ml) prevented enzyme activation by both detergents and UDP-N-acetyl glucosamine. When BSA was omitted and bilirubin dissolved in dimethyl sulfoxide, UDP-N-acetyl glucosamine failed to enhance GT activity, and activation by detergents was only 15-25% of that observed in the presence of optimal concentrations of BSA. When rat albumin was substituted for BSA, a similar dose-related inhibition of in vitro bilirubin conjugation by untreated microsomes was observed, although at any given albumin concentration, GT activity was lower with rat than with bovine albumin. Additionally, both detergents and UDP-N-acetyl glucosamine produced similar GT activation regardless of the rat albumin concentration. Finally, these effects of BSA and rat albumin could not be reproduced when beta-lactoglobulin was employed and/or when p-nitrophenol was the acceptor substrate of GT. These findings indicate that albumin, in particular BSA, profoundly and selectively influences the in vitro activity of microsomal GT toward bilirubin as the acceptor substrate.

Further studies on the properties of bile acids. II. Effect of bile acids on the reactivity of adrenergic and cholinergic receptors in rat intestine

The effects of bile acids (deoxycholic, cholic and dehydrocholic) were studied on the action of certain autonomic system drugs (isoprenaline, adrenaline, noradrenaline and acetylcholine). It was also tried to explain the causes of these changes in the light of the results of experiments with the widely used antagonists of adrenergic and cholinergic receptors. The experiments were carried out on isolated rat intestine by the method of Magnus. It was found that bile acids decreased the relaxing effect of isoprenaline and caused inversion of the action of adrenaline and noradrenaline on the intestine. Changes in the action of catecholamines are caused by stimulation of alpha-adrenergic receptors enhanced by bile acids, with a simultaneous decreased stimulation of beta-receptors. Bile acids cause also an increase of the effect of acetylcholine on the intestine.

Evidence for size and charge permselectivity of rat ascending colon. Effects of ricinoleate and bile salts on oxalic acid and neutral sugar transport

We have measured unidirectional transmural fluxes of oxalate and neutral sugars across rat ascending colon in vitro, under short-circuit conditions, to characterize permeability barriers selective for size and charge. Ionic oxalate appears to be transported preferentially to sodium oxalate. Mucosal addition of taurocholate (1 mM), deoxycholate (1 mM), or ricinoleate (1 mM) increased bidirectional oxalate fluxes, and the ricinoleate effects were independent of medium calcium. Bidirectional fluxes of uncharged sugar molecules fell sharply at molecular weights above 76 (molecular radius above 3 A), and oxalate transport was retarded relative to that of uncharged molecules of similar size, suggesting that there is both size and charge permselectivity. Ricinoleate increased fluxes of all neutral molecules tested but changed neither the exclusion limits nor the cation selectivity of the epithelium. Bile salts and ricinoleate increase oxalate transport, probably by making more channels available, but do not alter size and charge selectivity.

Structural restriction in bile acids and non-ionic detergents for promotion of heparin absorption from rat gastro-intestinal tract

Selected non-ionic surfactants of the polyoxyethylene ether series as well as selected bile acids elicit plasma clearing activity (PC) after oral heparin administration by action on the gastro-intestinal mucosa. Evidence obtained indicates that certain structural characteristics are needed for promoting heparin absorption, since this effect is observed with some but not all non-ionic detergents (cetyl and stearyl ethers but not lauryl) and bile components (deoxycholic, chenodeoxycholic and cholic acids, but not ursodeoxycholic or dehydrocholic acids or lecithin). It is suggested that a specific mechanism of action is involved.

Soluble phosphatidylinositol phosphodiesterase in normal and denervated fast and slow muscles of the rat

Phosphatidylinositol phosphodiesterase activity was determined in cytosol prepared from rat slow (soleus) and fast (extensor digitorum longus) muscles. The substrate was prepared by incubation of sarcoplasmic reticulum with myo-[2-3H]inositol. The enzyme hydrolysed both membrane-bound and extracted phosphatidylinositol. The activity determined with the isolated phospholipid exhibited an optimum at pH 5.5. Ca2+ ions stimulated the activity. The enzyme specific activity was higher in cytosol prepared from soleus muscle than in that from extensor digitorum longus muscle. After section of the motor nerve, the activity of the enzyme increased in both muscles up to 36 h and then declined. A function for this enzyme in the control of acetylcholine sensitivity in muscle is discussed.