Creatine transporter protein content, localization, and gene expression in rat skeletal muscle

The present study examined the gene expression and cellular localization of the creatine transporter (CreaT) protein in rat skeletal muscle. Soleus (SOL) and red (RG) and white gastrocnemius (WG) muscles were analyzed for CreaT mRNA, CreaT protein, and total creatine (TCr) content. Cellular location of the CreaT protein was visualized with immunohistochemical analysis of muscle cross sections. TCr was higher (P <= 0.05) in WG than in both RG and SOL, and was higher in RG than in SOL. Total CreaT protein content was greater (P <= 0.05) in SOL and RG than in WG. Two bands (55 and 70 kDa) of the CreaT protein were found in all muscle types. Both the 55-kDa (CreaT-55) and the 70-kDa (CreaT-70) bands were present in greater (P <= 0.05) amounts in SOL and RG than in WG. SOL and RG had a greater amount (P <= 0.05) of CreaT-55 than CreaT-70. Immunohistochemical analysis revealed that the CreaT was mainly associated with the sarcolemmal membrane in all muscle types. CreaT mRNA expression per microgram of total RNA was similar across the three muscle types. These data indicate that rat SOL and RG have an enhanced potential to transport Cr compared with WG, despite a higher TCr in the latter.

Steroid 21-hydroxylase expression in cultured rat astrocytes

Over the past decade or so it has become widely recognised that the brain is a significant steroidogenic organ. Many publications have highlighted the ability of the brain to synthesise and interconvert a large number of steroid products including cholesterol, progesterone and testosterone. In this study, in vitro experiments were performed to determine if 21-hydroxylation of steroids is undertaken by rat brain astrocytes in culture. This is a common reaction that occurs in the adrenal gland and other organs in mammals, catalysing the conversion of pregn-4-ene-3,20-dione (progesterone) to 21-hydroxypregn-4-ene-3,20-dione (deoxycorticosterone).

Previous reports have indicated that 21-hydroxylation occurs within the rat brain, however, the precise identity of the cells expressing 21-hydroxylase has not yet been determined. Several metabolites, such as 5α-pregnan-3α-ol-20-one (tetrahydroprogesterone) and 3α,21-dihydroxy-5-pregnan-20-one (tetrahydrodeoxycorticosterone) were of particular interest because of their modulatory role in neuronal function, such as their agonist activity at γ-aminobutyric acid (GABA_A) receptors.

Evidence was obtained for the expression of peripheral 21-hydroxylase enzyme (P450c21) in cultured rat brain astrocytes by a combination of mass spectroscopy and molecular biology techniques. This is a significant finding as expression of 21-hydroxylase within astrocytes may be indicative of a wider role for these cells in modulating neuronal behaviour.

The effect of repeated pulses of light at the same time on period responses of the rat circadian pacemaker.

A consequence of simple velocity-based models is that, in response to light pulses, the circadian period should adjust inversely to phase. In addition, because of the interaction of circadian period and phase response, earlier circadian period changes should modify later circadian period changes. The literature contains few mentions of response curves of circadian period responses following light pulses. Rats were exposed to four pulses of light (60 minutes, 1000 lux) at the same circadian time, a minimum of 26 days apart; we assessed period responses and possible bias in the period-response curve. Modulation of circadian period following light-induced phase responses was examined by assessing the period of running wheel activity onset. Phase and circadian period were not consistently found to share an inverse relationship. Moreover, biases in initial period tended to be increased by the experimental protocol regardless of circadian time of pulse. Rats with a short initial (highvelocity) period had a lengthened period, while rats with a long initial period (low velocity) tended to have a reduce period. However, rats with a long initial period were phase delay biased, not phase advance biased. These results do not support a simple velocity model of the pacemaker.

AMP-activated protein kinase activates transcription of the UCP3 and HKII genes in rat skeletal muscle

AMP-activated protein kinase (AMPK) has recently emerged as a key signaling protein in skeletal muscle, coordinating the activation of both glucose and fatty acid metabolism in response to increased cellular energy demand. To determine whether AMPK signaling may also regulate gene transcription in muscle, rats were given a single subcutaneous injection (1 mg/g) of the AMP analog 5-aminoimidazole-4-carboxamide-1-ß-D-ribonucleoside (AICAR). AICAR injection activated (P < 0.05) AMPK-α₂ (~2.5-fold) and transcription of the uncoupling protein-3 (UCP3, ~4-fold) and hexokinase II (HKII, ~10-fold) genes in both red and white skeletal muscle. However, AICAR injection also elicited (P < 0.05) an acute drop (60%) in blood glucose and a sustained (2-h) increase in blood lactate, prompting concern regarding the specificity of AICAR on transcription. To maximize AMPK activation in muscle while minimizing potential systemic counterregulatory responses, a single-leg arterial infusion technique was employed in fully conscious rats. Relative to saline-infused controls, single-leg arterial infusion of AICAR (0.125, 0.5, and 2.5 µg · g^-1 · min^-1 for 60 min) induced a dose-dependent increase (2- to 4-fold, P < 0.05) in UCP3 and HKII transcription in both red and white skeletal muscle. Importantly, AICAR infusion activated transcription only in muscle from the infused leg and had no effect on blood glucose or lactate levels. These data provide evidence that AMPK signaling is linked to the transcriptional regulation of select metabolic genes in skeletal muscle.

Interaction of exercise and diet on GLUT-4 protein and gene expression in type I and type II rat skeletal muscle

We determined the interaction of exercise and diet on glucose transporter (GLUT-4) protein and mRNA expression in type I (soleus) and type II [extensor digitorum longus (EDL)] skeletal muscle. Forty-eight Sprague Dawley rats were randomly assigned to one of two dietary conditions: high-fat (FAT, n =24) or high-carbohydrate (CHO, n =24). Animals in each dietary condition were allocated to one of two groups: control (NT, n =8) or a group that performed 8 weeks of treadmill running (4 sessions week^–1 of 1000 m @ 28 m min^–1 , RUN, n =16). Eight trained rats were killed after their final exercise bout for determination of GLUT-4 protein and mRNA expression: the remainder were killed 48 h after their last session for measurement of muscle glycogen and triacylglycerol concentration. GLUT-4 protein expression in NT rats was similar in both muscles after 8 weeks of either diet. However, there was a main effect of training such that GLUT-4 protein was increased in the soleus of rats fed with either diet (P < 0.05) and in the EDL in animals fed with CHO (P < 0.05). There was a significant diet–training interaction on GLUT-4 mRNA, such that expression was increased in both the soleus (100% ↑P < 0.05) and EDL (142% ↑P < 0.01) in CHO-fed animals. Trained rats fed with FAT decreased mRNA expression in the EDL (↓ 45%, P < 0.05) but not the soleus (↓ 14%, NS). We conclude that exercise training in CHO-fed rats increased both GLUT-4 protein and mRNA expression in type I and type II skeletal muscle. Despite lower GLUT-4 mRNA in muscles from fat-fed animals, exercise-induced increases in GLUT-4 protein were largely preserved, suggesting that control of GLUT-4 protein and gene expression are modified independently by exercise and diet.

5`-aminoimidazole-4-carboxyamide-ribonucleoside- activated glucose transport is not prevented by nitric oxide synthase inhibition in rat isolated skeletal muscle

1. The nucleoside intermediate 5'-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) activates skeletal muscle AMP-activated protein kinase (AMPK) and increases glucose uptake. The AMPK phosphorylates neuronal nitric oxide synthase (nNOS)µ in skeletal muscle fibres. There is evidence that both AMPK and nNOSµ may be involved in the regulation of contraction-stimulated glucose uptake.
2. We examined whether both AICAR- and contraction-stimulated glucose uptake were mediated by NOS in rat skeletal muscle.
3. Rat isolated epitrochlearis muscles were subjected in vitro to electrically stimulated contractions for 10 min and/or incubated in the presence or absence of AICAR (2 mmol/L) or the NOS inhibitor NG-monomethyl-l-arginine (l-NMMA; 100 µmol/L).
4. Muscle contraction significantly (P < 0.05) altered the metabolic profile of the muscle. In contrast, AICAR and l-NMMA had no effect on the metabolic profile of the muscle, except that AICAR increased muscle 5'-aminoimidazole-4-carboxyamide-ribonucleotide (ZMP) and AICAR content. Nitric oxide synthase inhibition caused a small but significant (P < 0.05) reduction in basal 3-O-methylglucose transport, which was observed in all treatments. 5'-Aminoimidazole-4-carboxyamide-ribonucleoside significantly increased (P < 0.05) glucose transport above basal, with NOS inhibition decreasing this slightly (increased by 209% above basal compared with 184% above basal with NOS inhibition). Contraction significantly increased glucose transport above basal, with NOS inhibition substantially reducing this (107% increase vs 31% increase). 5'-Aminoimidazole-4-carboxyamide-ribonucleoside plus contraction in combination were not additive on glucose transport.
5. These results suggest that NO plays a role in basal glucose uptake and may regulate contraction-stimulated glucose uptake. However, NOS/nitric oxide do not appear to be signalling intermediates in AICAR-stimulated skeletal muscle glucose uptake.

Differential effects of arginine, glutamate and phosphoarginine on Ca2+-activation properties of muscle fibres from crayfish and rat

The effects of two amino acids, arginine which has a positively charged side-chain and glutamate which has a negatively charged side-chain on the Ca²⁺-activation properties of the contractile apparatus were examined in four structurally and functionally different types of skeletal muscle; long- and short-sarcomere fibres from the claw muscle of the yabby (a freshwater decapod crustacean), and fast- and slow-twitch fibres from limb muscles of the rat. Single skinned fibres were activated in carefully balanced solutions of different pCa (-log₁₀[Ca²⁺]) that either contained the test solute (“test”) or not (“control”). The effect of phosphoarginine, a phosphagen that bears a nett negative charge, was also compared to the effects of arginine. Results show that (i) arginine (33-36 mmol l^-1) significantly shifted the force–pCa curve by 0.08–0.13 pCa units in the direction of increased sensitivity to Ca²⁺-activated contraction in all fibre types; (ii) phosphoarginine (9–10 mmol l^-1) induced a significant shift of the force–pCa curve by 0.18–0.24 pCa units in the direction of increased sensitivity to Ca²⁺ in mammalian fast- and slow-twitch fibres, but had no significant effects on the force–pCa relation in either long- or short-sarcomere crustacean fibres; (iii) glutamate (36–40 mmol l^-1), like arginine affected the force–pCa relation of all fibre types investigated, but in the opposite direction, causing a significant decrease in the sensitivity to Ca²⁺-activated contraction by 0.08–0.19 pCa units; (iv) arginine, phosphoarginine and glutamate had little or no effect on the maximum Ca²⁺-activated force of crustacean and mammalian fibres. The results suggest that the opposing effects of glutamate and arginine are not related to simply their charge structure, but must involve complex interactions between these molecules, Ca²⁺ and the regulatory and other myofibrillar proteins.

Omega 6 to omega 3 fatty acid imbalance early in life leads to persistant reductions in DHA levels in glycerophospholipids in rat hypothalamus even after long-term omega 3 fatty acid repletion

Failure to provide omega 3 fatty acids in the perinatal period results in alterations in nerve growth factor levels, dopamine production and  permanent elevations in blood pressure. The present study investigated whether changes in brain (i.e., hypothalamus) glycerophospholipid fatty acid profiles induced by a diet rich in omega 6 fatty acids and very low in alpha-linolenic acid (ALA) during pregnancy and the perinatal period could be reversed by subsequent feeding of a diet containing ALA. Female rats (6 per group) were mated and fed either a low ALA diet or a control diet containing ALA throughout pregnancy and until weaning of the pups at 3 weeks. At weaning, the pups (20 per group) remained on the diet of their mothers until 9 weeks, when half the pups were switched onto the other diet, thus generating four groups of animals. At 33 weeks, pups were killed, the hypothalamus dissected from the male rats and analysed for glycerophospholipid fatty acids. In the animals fed the diet with very little ALA and then re-fed the control diet containing high levels of ALA for 24 weeks, the DHA levels were still significantly less than the control values in PE, PS and PI fractions, by 9%, 18% and 34%, respectively. In this group, but not in the other dietary groups, ALA was detected in all glycerophospholipid classes at 0.2–1.7% of the total fatty acids. The results suggest that omega 6–3 PUFA imbalance early in life leads to irreversible changes in hypothalamic composition. The increased ALA and reduced DHA proportions in the animals re-fed ALA in later life are consistent with a dysfunction or down-regulation of the conversion of ALA to 18:4n-3 by the delta-6 desaturase.

The influence of magnetic fields exposure on neurite outgrowth in PC12 rat pheochromocytoma cells

The aim of present work was to investigate the influence of magnetic fields exposure on neurite outgrowth in PC12 cells. The neurite number per cell, length of neurites and directions of neurite growth with respect to the direction of the magnetic field were analyzed after exposure to 50 Hz electromagnetic field for 96 h. A promotion was observed under a weak field (0.23 mT), as the average number of neurites per cell increased to 2.38±0.06 compared to 1.91±0.07 neurites/cell of the control dishes, while inhibition and directional outgrowth was evident under a relatively stronger field (1.32 mT). Our work shows that biological systems can be very sensitive to the strength of electromagnetic field.

Analysis of cardioprotective effects using purified Saliva miltiorrhiza extract on isolated rat hearts

The purpose of the current study is to evaluate the cardioprotective effects of purified Salvia miltiorrhiza extract (PSME) on myocardial ischemia/reperfusion injury in isolated rat hearts. Hearts were excised and perfused at constant flow (7 – 9 ml · min⁻¹) via the aorta. Non-recirculating perfusion with Krebs-Henseleit (KH) solution was maintained at 37°C and continuously gassed with 95% O₂ and 5% CO₂. KH solution with or without PSME (100 mg per liter solution) was used after 30-min zero-flow ischemia for the PSME and control group, respectively. Left ventricular (LV) developed pressure; its derivatives, diastolic pressure, and so on were continuously recorded via a pressure transducer attached to a polyvinylchloride balloon that was placed in the left ventricle through an incision in the left atrium. PSME treated hearts showed significant postischemic contractile function recovery (developed pressure recovered to 44.2 ± 4.9% versus 17.1 ± 5.7%, P<0.05; maximum contraction recovered to 57.2 ± 5.9% versus 15.1 ± 6.3%, P<0.001; maximum relaxation restored to 69.3 ± 7.3% versus 15.4 ± 6.3%, P<0.001 in the PSME and control group, respectively). Significant elevation in end-diastolic pressure, which indicated LV stiffening in PSME hearts might have resulted from the excess high dose of PSME used. Further study will be conducted on the potential therapeutic value with lower dose of PSME on prevention of ischemic heart disease.

Effects of purified herbal extract of Saliva miltiorrhiza on ischemic rat myocardium after acute myocardial infarction

In the current study, we compared purified Salvia miltiorrhiza extract (PSME) with Angiotensin-converting enzyme inhibitor, Ramipril, in in vitro experiments and also in vivo using animal model of myocardial infarction. PSME was found to have a significantly higher trolox equivalent antioxidant capacity which indicated a great capacity for scavenging free radicals. PSME could also prevent pyrogallo red bleaching and DNA damage.

After 2 weeks treatment with PSME or Ramipril, survival rates of rats with experimental myocardial infarction were marginally increased (68.2% and 71.4%) compared with saline (61.5%). The ratios of infarct size to left ventricular size in both PSME-and Ramipril-treated rats were significantly less than that in the saline-treated group. Activity of cardiac antioxidant enzyme superoxide dismutase (SOD) was significant higher while level of Thiobarbituric acid-reactive substances (TBARs) was lower in the PSME treated group. Purified and standardized Chinese herb could provide an alternative regimen for the prevention of ischemic heart disease.

Simultaneous determination of the lactone and carboxylate forms of irintecan (CPT-11) and its actie metabolite SN-38 by high-performance liquid chromatography: Application to plasma pharmacokinetic studies in the rat.

Irinotecan (CPT-11) and its main metabolite SN-38 are potent anticancer derivatives of camptothecin (CPT), with active lactone and inactive carboxylate forms coexisting. A simple and sensitive HPLC method using the ion-pairing reagent tetrabutylammonium hydrogen sulfate (TBAHS) was developed to simultaneously determine all four analytes in rat plasma samples. Camptothecin (CPT) was used as internal standard. The mobile phase was 0.1 M potassium dihydrogen phosphate containing 0.01 M TBAHS (pH 6.4)–acetonitrile (75:25, v/v). Separation of the compounds was carried out on a Hypersil C18 column, monitored at 540 nm (excitation wavelength at 380 nm). All four compounds gave linear response as a function of concentration over 0.01–10 μM. The limit of quantitation in rat plasma was 0.01, 0.008, 0.005 and 0.005 μM for CPT-11 lactone, CPT-11 carboxylate, SN-38 lactone and SN-38 carboxylate, respectively. The method was successfully used in the study on the effect of coadministered thalidomide on the plasma pharmacokinetics of CPT-11 and SN-38 in rats. Coadministered thalidomide (100 mg/kg body weight by intraperitoneal injection) significantly increased the AUC_0–10h values of CPT-11 lactone and CPT-11 carboxylate by 32.6% and 30.3 %, respectively, (P < 0.01), but decreased the values by 19.2% and 32.4% for SN-38 lactone and carboxylate, respectively, (P < 0.05). Accordingly, the value of total body clearance (CL) of CPT-11 lactone was significantly lower in combination group compared to the control (1.329 versus 1.837 L/h/kg, P = 0.0002). Plasma t_1/2β values for SN-38 lactone and carboxylate were significantly (P < 0.01) smaller in rats with coadministered thalidomide, as compared to rats receiving CPT-11 alone. Further studies are needed to explore the underlying mechanisms for the observed kinetic interaction between CPT-11 and thalidomide.

Use of in vitro critical inhibitory concentration, a novel approach to predict in vivo synergistic bactericidal effect of combined amikacin and piperacillin against pseudomonas aeruginosa in a systemic rat infection model

PURPOSE: This study was undertaken to explore the use of in vitro critical inhibitory concentration (CIC) as a surrogate marker relating the pharmacokinetic (PK) parameters to in vivo bactericidal synergistic effect [pharmacodynamic (PD)] of amikacin + piperacillin combination against Pseudomonas aeruginosa in a systemic rat infection model. METHODS: The in vitro antibacterial activities of amikacin and piperacillin, alone and in combinations at various ratios of the concentrations, were tested against a standard [5 x 10(5) colony-forming units (CFU)/ml] and a large (1.5 x 10(8) CFU/ml) inoculum of P. aeruginosa ATCC 9027 using a modified survival-time method. The CIC of each individual antibiotic for the different combinations was determined using a cup-plate method. In vivo studies were performed on Sprague-Dawley rats using a systemic model of infection with P. aeruginosa ATCC 9027. PK profiles and in vivo killing effects of the combination at different dosing ratios were studied. RESULTS: An inoculum effect was observed with the antibiotics studied. Synergy was seen against both the inocula at the following concentration ratios: 70% C(ami) + 30% C(pip) and 75% C(ami) + 25% C(pip), where C(ami) and C(pip) are the concentrations of amikacin and piperacillin to produce a 1000-fold decrease in bacterial population over 5 h, respectively. The CIC values determined corroborated with the order of in vitro bacterial killing observed for the antibiotic combinations. The dosing ratio of 12.6 mg/kg amikacin + 36 mg/kg piperacillin (a 70:30 ratio of the individual doses) exhibited the greatest killing in vivo when compared to the other ratios. The PK-PD relationships were described by simple, linear regression equations using the area under the in vivo killing curve as a PD marker and the AUCIC(ami)/CIC(ami) + AUCIC(pip)/CIC(pip), AUC(ami)/CIC(ami) + AUC(pip)/CIC(pip), C(max,ami)/CIC(ami) + C(max,pip)/CIC(pip), and AUCIC(ami)/MIC(ami) + AUCIC(pip)/MIC(pip) as PK markers for the amikacin + piperacillin combination. CONCLUSION: The combination of amikacin and piperacillin exhibited synergistic killing effect on P. aeruginosa that could be modeled using CIC as a surrogate marker relating the PK parameters to in vivo bactericidal effect.