Retigabine stimulates human KCNQ2/Q3 channels in the presence of bupivacaine

BACKGROUND: Inhibition of KCNQ2/Q3 channels may cause convulsion in humans. The interaction of bupivacaine with these channels is unknown. The anticonvulsant retigabine activates KCNQ2/Q3 channels and may reverse inhibitory actions of bupivacaine. Potassium channel stimulation may thus constitute a novel approach to treat local anesthetic-induced seizures. The aim of this study was to characterize bupivacaine effects on KCNQ2/Q3 channels and to investigate whether retigabine reverses the effects of the local anesthetic. METHODS: KCNQ2/Q3 channels were transiently expressed in Chinese hamster ovary cells. The effects of bupivacaine and retigabine were studied with the patch-clamp technique. RESULTS: Bupivacaine inhibited KCNQ2/Q3 channels in a concentration-dependent and reversible manner. The concentration-response curve was described by a Hill equation (IC50 = 173 +/- 7 microm, Hill coefficient = 1.4 +/- 0.1, mean +/- SEM, n = 37). The inhibitory effect did not differ between bupivacaine and levobupivacaine (42 +/- 4%, n = 7, versus 42 +/- 5%, n = 10; P > 0.05). Ropivacaine was four times less potent than bupivacaine. The inhibition of KCNQ2/Q3 channels by bupivacaine resulted in a significant and reversible depolarization of the membrane potential. Retigabine (300 nm-10 microm) reversed the inhibitory action of bupivacaine on KCNQ2/Q3 channels as well as the depolarization of the membrane potential. CONCLUSIONS: The anticonvulsant retigabine at nanomolar concentrations reverses the inhibitory effect of micromolar concentrations of bupivacaine. Our results allow the hypothesis that activation of KCNQ2/Q3 channels by retigabine may offer a novel therapeutic approach for the treatment of bupivacaine-induced seizures.     

Block of Human Heart hH1 Sodium Channels by the Enantiomers of Bupivacaine

Background: S(-)-bupivacaine reportedly exhibits lower cardiotoxicity but similar local anesthetic potency compared with R (+)-bupivacaine. The bupivacaine binding site in human heart (hH1) Na+ channels has not been studied to date. The authors investigated the interaction of bupivacaine enantiomers with hH1 Na+ channels, assessed the contribution of putatively relevant residues to binding, and compared the intrinsic affinities to another isoform, the rat skeletal muscle ([mu]1) Na+ channel.

Methods: Human heart and [mu]1 Na+ channel [alpha] subunits were transiently expressed in HEK293t cells and investigated during whole cell voltage-clamp conditions. Using site-directed mutagenesis, the authors created point mutations at positions hH1-F1760, hH1-N1765, hH1-Y1767, and hH1-N406 by introducing the positively charged lysine (K) or the negatively charged aspartic acid (D) and studied their influence on state-dependent block by bupivacaine enantiomers.

Results: Inactivated hH1 Na+ channels displayed a weak stereoselectivity with a stereopotency ratio (+/-) of 1.5. In mutations hH1-F1760K and hH1-N1765K, bupivacaine affinity of inactivated channels was reduced by ~ 20- to 40-fold, in mutation hH1-N406K by ~ sevenfold, and in mutations hH1-Y1767K and hH1-Y1767D by ~ twofold to threefold. Changes in recovery of inactivated mutant channels from block paralleled those of inactivated channel affinity. Inactivated hH1 Na+ channels exhibited a slightly higher intrinsic affinity than [mu]1 Na+ channels.     

Structural Requirements of Human Ether-a-go-go-related Gene Channels for Block by Bupivacaine

Background: Local anesthetics interact with human ether-a-go-go-related gene (HERG) channels via the aromatic amino acids Y652 and F656 in the S6 region. This study aimed to establish whether the residues T623, S624, and V625 residing deeper within the pore are also involved in HERG channel block by bupivacaine. In addition, the study aimed to further define the role of the aromatic residues Y652 and F656 in bupivacaine inhibition by mutating these residues to threonine.

Methods: Alanine and threonine mutants were generated by site-directed mutagenesis. Electrophysiologic and pharmacologic properties of wild-type and mutant HERG channels were established using two-electrode voltage-clamp recordings of Xenopus laevis oocytes expressing HERG channels.

Results: Tail currents at -120 mV through HERG wild-type channels were inhibited with an IC50 value of 132 +/- 22 [mu]m (n = 33). Bupivacaine (300 [mu]m) inhibited wild-type tail currents by 62 +/- 12% (n = 7). Inhibition of HERG tail currents by bupivacaine (300 [mu]m) was reduced by all mutations (P < 0.001). The effect was largest for F656A (inhibition 5 +/- 2%, n = 6) in the lower S6 region and for T623A (inhibition 13 +/- 4%, n = 9) near the selectivity filter. Introducing threonine at positions 656 and 652 significantly reduced inhibition by bupivacaine compared with HERG wild type (P < 0.001).     

Stereoselectivity of Bupivacaine in Local Anesthetic-sensitive Ion Channels of Peripheral Nerve

Background: The local anesthetic bupivacaine exists in two stereoisomeric forms, R(+)- and S(-)-bupivacaine. Because of its lower cardiac and central nervous system toxicity, attempts were made recently to introduce S(-)-bupivacaine into clinical anesthesia. We investigated stereoselective actions of R(+)- and S(-)-bupivacaine toward two local anesthetic-sensitive ion channels in peripheral nerve, the Na+ and the flicker K+ channel.

Methods: In patch-clamp experiments on enzymatically demyelinated peripheral amphibian nerve fibers, Na+ and flicker K+ channels were investigated in outside-out patches. Half-maximum inhibiting concentrations (IC50) were determined. For the flicker K+ channel, simultaneous block by R(+)-bupivacaine and S(-)-bupivacaine was analyzed for competition and association (k1) and dissociation rate constants (k-1) were determined.

Results: Both channels were reversibly blocked by R(+)- and S(-)-bupivacaine. The IC50 values (+/-SEM) for tonic Na+ channel block were 29 +/- 3 [mu]M and 44 +/- 3 [mu]M, respectively. IC50 values for flicker K+ channel block were 0.15 +/- 0.02 [mu]M and 11 +/- 1 [mu]M, respectively, resulting in a high stereopotency ratio (+/-) of 73. Simultaneously applied enantiomers competed for a single binding site. Rate constants k1 and k-1 were 0.83 +/- 0.13 x 106 M-1 [middle dot] s-1 and 0.13 +/- 0.03 s-1, respectively, for R(+)-bupivacaine and 1.90 +/- 0.20 x 106 M-1 [middle dot] s-1 and 8.3 +/- 1.0 s-1, respectively, for S(-)-bupivacaine.     

Kvβ1.3 Reduces the Degree of Stereoselective Bupivacaine Block of Kv1.5 Channels

Background: Kv[beta]1.3 subunit modifies the gating and the pharmacology of Kv1.5 channels, decreasing their sensitivity to block induced by drugs, suggesting that Kv[beta]1.3 competes with them for a binding site at Kv1.5 channels.

Methods: Currents generated by the activation of Kv1.5 and Kv1.5 + Kv[beta]1.3 channels expressed in HEK293 cells and Xenopus oocytes were recorded by using whole cell patch clamp and voltage clamp techniques.

Results: Block of Kv1.5, but not that produced on Kv1.5 + Kv[beta]1.3 channels, was voltage dependent. In both channels, bupivacaine block was time dependent. R(+)- and S(-)-bupivacaine blocked Kv1.5 with IC50 4.4 +/- 0.5 [mu]m (n = 15) and 39.8 +/- 8.2 [mu]m (n = 16; P < 0.05), respectively. These values increased fourfold for R(+)-bupivacaine (17.2 +/- 2.2 [mu]m) and twofold for S(-)-bupivacaine (71.9 +/- 11.5 [mu]m) in Kv1.5 + Kv[beta]1.3 channels. Therefore, the degree of stereoselectivity ([theta]) decreased from 9 to 4 in the presence of Kv[beta]1.3. The decrease in potency to block Kv1.5 + Kv[beta]1.3 channels was the result of a less stable interaction between bupivacaine enantiomers and channels. Differences in stereoselectivity in each situation were due to a more favorable interaction between the channel and R(+)-bupivacaine. In the presence of Kv[beta]1.3, stereoselectivity was abolished for V514A mutant channels (involved in bupivacaine binding but not in Kv[beta]1.3 binding) but not for L510A (part of Kv[beta]1.3 binding site).     

Motility Related to the Presence of Carnitine/Acetyl-Carnitine in Human Spermatozoa

Total carnitine, acetylcarnitine and carnitine acetyl transferase (E.C. 2.3.1.7) were measured in the plasma and spermatozoa fractions of 41 samples of human semen and the correlation with sperm motility and sperm density examined.
It was confirmed that the concentration of total carnitine as well as of acetylcarnitine was 2–25 times higher and the activity of carnitine acetyl transferase 20–15 fold higher in spermatozoa than in seminal plasma. Sperm motility correlated with the concentration of acetylcarnitine (r = 0.6, P < 0.01) and of total carnitine (r = 0.55, P < 0.01) but not with the concentration of free carnitine nor with the activity of carnitine acetyl transferase in the spermatozoa. No correlation was found between sperm motility and the concentrations of acetylcarnitine, free carnitine or total carnitine in the seminal plasma.
It is concluded that the amount of carnitine present in the spermatozoa probably provides a better index of epididymal function than the carnitine in the seminal plasma as the latter in influenced by af variable contribution from the other accessory sex organs.     

正常人类精子电压依赖性钙通道类型的分子生物学鉴别

目的:利用分子生物学技术对正常人类精子中电压依赖性钙通道的类型进行鉴别。方法:根据WHO标准用计算机辅助精液分析筛选出5例正常精子标本(前向运动精子>60%,活率>80%),混合后用上游法对精子进行优化。采用RT-PCR检测人类精子中电压依赖性钙通道的α亚单位。结果:α1A和α1D未检测出,而其他α亚单位,如α1H、α1G、α1E、α1B、α1C均有表达。结论:在正常人类精子中电压依赖性钙通道显著表达T型或非L型RNA,在精子运动和精子顶体反应中,细胞外的钙离子内流可能是通过T型或非L型电压依赖性钙通道介导的。     

Recombinant Human Erythropoietin Stimulates Production of Interleukin 2 by Whole Blood Cell Cultures of Hemodialysis Patients

Abstract: The impairment of function of human T lymphocytes, leading to an inappropriate cytokine production, is partially responsible for defective immunological response in hemodialysis patients (HD). Recent data suggest that recombinant human erythropoietin (rhEPO) may exert immunological effects. The aim of this study was to find out whether rhEPO treatment of the HD patients may have an effect on the interleukin 2 (IL-2) production by their whole blood cell cultures. The study was carried out in 10 HD patients receiving rhEPO for 6 months. Compared with the levels seen before the treatment, the concentration of IL-2 increased in the phytohemagglutinin-stimulated whole blood cell cultures of 7 of 10 patients under study. Addition of rhEPO in vitro to the whole blood cell cultures of the HD patients before implementation of erythropoietin confirmed that rhEPO is able to directly stimulate IL-2 production. Our studies show that the therapy with rhEPO affects IL-2 secretion.     

Dexamethasone Prolongs Local Analgesia after Subcutaneous Infiltration of Bupivacaine Microcapsules in Human Volunteers

Background: The addition of small amounts of dexamethasone to extended-release formulations of bupivacaine in microcapsules has been found to prolong local analgesia in experimental studies, but no clinical data are available.

Methods: In a double-blinded study, 12 healthy male volunteers were randomized to receive simultaneous subcutaneous injections of bupivacaine microcapsules with dexamethasone and bupivacaine microcapsules without dexamethasone in each calf. Local analgesia was assessed with a validated human pain model; main parameters evaluated were thermal, mechanical, and pain detection thresholds and suprathreshold responses to heat and mechanical stimulation. Measurements were performed every 2 h for the first 8 h and daily for the week after injection. Primary endpoints were evaluation of maximal analgesic effect, time of onset, and duration of analgesia. Summary measures (area under curve [AUC]) were considered best estimate of analgesia. Safety evaluations were performed daily for the first week and at 2 weeks, 6 weeks, and 6 months after injection.

Results: The addition of dexamethasone significantly prolonged local analgesia of bupivacaine microcapsules without influence on maximal analgesic effect. AUC in all thermal measurements and the sensory mechanical threshold were significantly increased between 1-7 days after drug injection in the group given dexamethasone compared with the group not given dexamethasone. No serious side effects were observed.     

Molecular Mechanisms of the Inhibitory Effects of Bupivacaine, Levobupivacaine, and Ropivacaine on Sarcolemmal Adenosine Triphosphate-sensitive Potassium Channels in the Cardiovascular System

Background: Sarcolemmal adenosine triphosphate-sensitive potassium (KATP) channels in the cardiovascular system may be involved in bupivacaine-induced cardiovascular toxicity. The authors investigated the effects of local anesthetics on the activity of reconstituted KATP channels encoded by inwardly rectifying potassium channel (Kir6.0) and sulfonylurea receptor (SUR) subunits.

Methods: The authors used an inside-out patch clamp configuration to investigate the effects of bupivacaine, levobupivacaine, and ropivacaine on the activity of reconstituted KATP channels expressed in COS-7 cells and containing wild-type, mutant, or chimeric SURs.

Results: Bupivacaine inhibited the activities of cardiac KATP channels (IC50 = 52 [mu]m) stereoselectively (levobupivacaine, IC50 = 168 [mu]m; ropivacaine, IC50 = 249 [mu]m). Local anesthetics also inhibited the activities of channels formed by the truncated isoform of Kir6.2 (Kir6.2[DELTA]C36) stereoselectively. Mutations in the cytosolic end of the second transmembrane domain of Kir6.2 markedly decreased both the local anesthetics' affinity and stereoselectivity. The local anesthetics blocked cardiac KATP channels with approximately eightfold higher potency than vascular KATP channels; the potency depended on the SUR subtype. The 42 amino acid residues at the C-terminal tail of SUR2A, but not SUR1 or SUR2B, enhanced the inhibitory effect of bupivacaine on the Kir6.0 subunit.     

Inhibition of Kv4.3/KChIP2.2 Channels by Bupivacaine and Its Modulation by the Pore Mutation Kv4.3V401I

Background: The transient outward current Ito is an important repolarizing K current in human ventricular myocardium mediated by Kv4.3 and KChIP2.2 subunits. Inhibition of Ito by amino-amide local anesthetics may be involved in severe cardiotoxic side effects. This study elucidates the molecular mechanisms of bupivacaine interaction with complexes formed by Kv4.3 and KChIP2.2 as well as the modulatory effect of KChIP2.2. For this purpose, the pharmacologic effects of bupivacaine on Kv4.3wt/KChIP2.2 channels and on the pore mutant Kv4.3V401I were investigated.

Methods: Kv4.3/KChIP2.2 cDNA was transiently expressed in Chinese hamster ovary cells. Site-directed mutagenesis and patch clamp experiments were performed to analyze the effects of bupivacaine on wild-type and mutant channels.

Results: Inhibition of Kv4.3wt/KChIP2.2 channels by bupivacaine was concentration-dependent and reversible. The IC50s for inhibition of the charge conducted by Kv4.3wt/KChIP2.2 channels by bupivacaine and levobupivacaine were 55 +/- 8 and 50 +/- 5 [mu]m, respectively. The local anesthetic accelerated macroscopic current decline of Kv4.3wt/KChIP2.2 and slowed recovery from inactivation without altering steady state inactivation. KChIP2.2 altered the response of Kv4.3wt channels to bupivacaine and bupivacaine modulated KChIP2.2 effects on Kv4.3wt channels. The pore mutation V401I slowed macroscopic current decline of Kv4.3 channels and recovery from inactivation, and it diminished modulation of gating by KChIP2.2. Bupivacaine inhibition of Kv4.3V401I resembled Kv4.3wt and was not changed by coexpression of KChIP2.2.     

Clinical Article Accumulation of PN1 and PN3 Sodium Channels in Painful Human Neuroma-Evidence from Immunocytochemistry

Summary. Summary.   Background: The axolemmal distribution and density of voltage-gated sodium channels largely determines the electrical excitability of sprouting neurites. Recent evidence suggests that accumulation of sodium channels at injured axonal tips may be responsible for ectopic axonal hyperexcitability and the resulting abnormal sensory phenomena of pain and paresthesias. For future improvement in pain management it is necessary to identify structurally significant generators of autorhythmicity. A first step in this regard will be to determine the predominant types of sodium channels in injured axons. The opportunity to test human specimens from painful and non-painful neuroma is of great value.   Methods: We employed immunocytochemical methods to investigate if two types of highly specific voltage-gated sodium channel subtypes could be detected in sections of human neuroma.   Findings: Both subtypes of sodium channels PN1 and PN3 accumulated abnormally in human neuromas. The immunoreactive pattern was more pronounced in painful neuromas. This is in contrast to previous reports that focused either on PN1 or PN3 as main generators of hyperexcitability induced pain.   Interpretation: Both, PN1 and PN3 seem to be involved in hyperexcitability induced pain. It can be expected that a variety of other highly specific voltage gated sodium channel subtypes will be detected in regenerating peripheral nerve in the near future, which contribute to the development of neuropathic pain states. Thus, in order to therapeutically control hyperexcitability induced neuropathic pain, it might be worthwhile to develop pharmaceuticals that can selectively block different sodium channel subtypes and subunits.  A review of the role of sodium channels in neuropathic pain is implemented in the discussion. Published online August 12, 2002     

Overexpression of Smurf2 Stimulates Endochondral Ossification Through Upregulation of β‐Catenin

Ectopic expression of Smurf2 in chondrocytes and perichondrial cells accelerated endochondral ossification by stimulating chondrocyte maturation and osteoblast development through upregulation of β‐catenin in Col2a1‐Smurf2 embryos. The mechanism underlying Smurf2‐mediated morphological changes during embryonic development may provide new mechanistic insights and potential targets for prevention and treatment of human osteoarthritis. Introduction : Our recent finding that adult Col2a1‐Smurf2 mice have an osteoarthritis‐like phenotype in knee joints prompted us to examine the role of Smurf2 in the regulation of chondrocyte maturation and osteoblast differentiation during embryonic endochondral ossification. Materials and Methods : We analyzed gene expression and morphological changes in developing limbs by immunofluorescence, immunohistochemistry, Western blot, skeletal preparation, and histology. A series of markers for chondrocyte maturation and osteoblast differentiation in developing limbs were examined by in situ hybridization. Results : Ectopic overexpression of Smurf2 driven by the Col2a1 promoter was detected in chondrocytes and in the perichondrium/periosteum of 16.5 dpc transgenic limbs. Ectopic Smurf2 expression in cells of the chondrogenic lineage inhibited chondrocyte differentiation and stimulated maturation; ectopic Smurf2 in cells of the osteoblastic lineage stimulated osteoblast differentiation. Mechanistically, this could be caused by a dramatic increase in the expression of β‐catenin protein levels in the chondrocytes and perichondrial/periosteal cells of the Col2a1‐Smurf2 limbs. Conclusions : Ectopic expression of Smurf2 driven by the Col2a1 promoter accelerated the process of endochondral ossification including chondrocyte maturation and osteoblast differentiation through upregulation of β‐catenin, suggesting a possible mechanism for development of osteoarthritis seen in these mice.     

Smooth Muscle Effects of Lidocaine, Prilocaine, Bupivacaine and Etidocaine on the Human Umbilical Artery

The smooth muscle effects on human umbilical arteries of four different local anaesthetic agents-lidocaine. etidocaine, prilocaine and bupivacaine-were studied. Lidocaine and etidocaine relaxed the arteries. etidocaine more profoundly than lidocaine. Prilocaine in the concentration range 10-1,000 μg/ml caused pronounced contractions. Bupivacaine consistently evoked a contractile response in the concentration range 5–25 pg/ml. but at lower and higher concentrations the response to this drug was inconsistent. The concentrations of lidocaine were determined in six human umbilical arteries following maternal epidural block with this agent and were found to be 0.1-1.7 μg/g tissue. The contractile actions of prilocaine and bupivacaine on the human umbilical arteries are undesirable and might be hazardous if high concentrations are attained, e.g. during paracervical block.     

Presence of the C3b Complement Receptor (CR1) Antigen in the Glomerular Basement Membrane of Human Fetal Kidneys

The distribution pattern of the C_3b receptor (CR1) antigen,one of the earliest differentiation markers of the podocyteplasma membrane, has been studied during human renal ontogenesisby indirect immunofluorescence and immunoelectronmicroscopyusing Fab'2 fragments ofanti-CR1 antibodies. CR1 antigen hasbeen detected at the open-stage glomerulus, which precedes constrictionof the vascular pole, along the capillary wall, in a thick andhomogeneous pattern of staining. By immunoelectronmicroscopy,CR1 antigen was present on the porocyte plasma membrane towardsthe glomerular basement membrane (GBM), and diffusely distributedwithin the GBM according to a decreasing intensity gradientfrom podocytes to endothelial cells. At a later stage of differentiation(‘closed’ glomerulus stage) when constriction ofthe vascular pole has occurred, the podocyte plasma membraneappeared diffusely labelled for CR1;the GBM was also stainedwith a decreasing intensity gradient from podocytes to endothelialcells. This result indicates that a plasma membrane receptorbelonging to the cell coat of podocytes can be found in theextracellular space within the GBM. Thus the antigenic repertoireof the GBM of human fetal kidney comprises antigens of constituentmolecules of the extracellular matrix and planted antigens originatingfrom adjacent cells.     

Osteogenic Protein-1 Stimulates mRNA Levels of BMP-6 and Decreases mRNA Levels of BMP-2 and -4 in Human Osteosarcoma Cells

Bone morphogenetic proteins (BMPs) are novel growth and differentiation factors that act on mesenchymal stem cells to initiate new bone formation in vivo and promote the growth and differentiation of cells in the osteoblastic lineage. In the present study, we examined the effects of recombinant human osteogenic protein-1 (also known as BMP-7) on the expression of related members of the BMP family using SaOS-2 and U2-OS, two human osteosarcoma cell strains. Evaluation of BMP-2, -4, and -6 mRNA expression indicates that OP-1 stimulated the mRNA levels of BMP-6 in both SaOS-2 cells (threefold) and U2-OS cells (fivefold) after 24 hours of treatment, while decreasing the mRNA levels of BMP-4 in SaOS-2 cells (80%) and BMP-2 and BMP-4 in U2-OS cells by 50% and 72%, respectively. BMP-2 mRNA expression, as examined by Northern blot analysis, was below detectable limits in SaOS-2 cultures. These results demonstrate that OP-1 modulates the mRNA expression of related members of the BMP family, suggesting a possible mode of action of OP-1 on the growth and differentiation of cells in the osteoblastic lineage in vitro. Received: 7 May 1996 / Accepted: 24 September 1996