Upper limb exosuit cable routing optimization.

Exosuits are emerging as promising in assisting with activities of daily living. In the design phase of an exosuit, it is fundamental to maximize its portability. The goal of this work was to identify the best cable routing configuration for an upper limb cable-driven exosuit to assist elbow flexion. Simulations were run in OpenSim. Different cable configurations were evaluated. The goal was to minimize the overall tension of the cables to reduce the device's power consumption and torque requirements. The optimal configuration was evaluated in simulation for different percentages of assistance to study its effects in terms of muscle activation and joint reaction forces. We then tested three different configurations on a test bench to both evaluate the motor current and their effect on the pronation/supination of the elbow. Simulation results suggested that a double cable configuration might help to lower the motor torque and power consumption. This conclusion was supported by the experimental results, in which the motor current was reduced by 12.5% with respect to the single cable configuration. Simulation results also showed that the optimal configuration lowered muscle activation without greatly affecting joint reactions at the elbow, even though it might cause unwanted pronation/supination, as experimental results confirmed. However, since a double configuration results in greater complexity and reduced efficiency, single-cable solutions still represent a good option.

Effect of supplementation with vitamins D3 and K2 on undercarboxylated osteocalcin and insulin serum levels in patients with type 2 diabetes mellitus: a randomized, double-blind, clinical trial.

BACKGROUND: Patients with type 2 diabetes mellitus (T2DM) are characterized by chronic hyperglycemia as a consequence of decreased insulin sensitivity, which contributes to bone demineralization and could also be related to changes in serum levels of osteocalcin and insulin, particularly when coupled with a deficiency in the daily consumption of vitamins D3 and K2. The objective of this study was to evaluate the effect of vitamin D3 and vitamin K2 supplements alone or in combination on osteocalcin levels and metabolic parameters in patients with T2DM. METHODS: A double-blind, randomized clinical trial was carried out in 40 patients aged between 30 and 70 years old for 3 months. Clinical and laboratory assessment was carried out at the beginning and at the end of the treatment. The patients were divided into three groups: (a) 1000 IU vitamin D3 + a calcinated magnesium placebo (n = 16), (b) 100 µg of Vitamin K2 + a calcinated magnesium placebo (n = 12), and (c) 1000 IU vitamin D3 + 100 µg vitamin K2 (n = 12). RESULTS: After treatment in the total studied population, a significant decrease in glycemia (p = 0.001), HOMA-IR (Homeostatic model assessment-insulin resistance) (p = 0.040), percentage of pancreatic beta cells (p < 0.001), uOC/cOC index and diastolic blood pressure (p = 0.030) were observed; in vitamin D3 group, differences in serum undercarboxylated osteocalcin (p = 0.026), undercarboxylated to carboxylated osteocalcin index (uOC/cOC) (p = 0.039) glucose (p < 0.001) and  % of functional pancreatic beta cells (p < 0.001) were demonstrated. In vitamin K2 group a significant decrease in glycemia (p = 0.002), HOMA-IR (p = 0.041), percentage of pancreatic beta cells (p = 0.002), and in cOC (p = 0.041) were observed, conversely cOC concentration was found high. Finally, in the vitamins D3 + K2 a significant decrease in glycemia (p = 0.002), percentage of pancreatic beta cells (p = 0.004), and in the uOC/cOC index (p = 0.023) were observed. CONCLUSION: Individual or combined supplementation with vitamins D3 and K2 significantly decreases the glucose levels and  % of functional pancreatic beta cells, while D3 and D3 + K2 treatments also induced a reduction in the uOC/cOC index. Only in the group with vitamin D3 supplementation, it was observed a reduction in undercarboxylated osteocalcin while vitamin K2 increased the carboxylated osteocalcin levels.Trial registration NCT04041492.

Macrophage migration inhibitory factor (MIF): genetic evidence for participation in early onset and early stage rheumatoid arthritis.

Macrophage migration inhibitory factor (MIF) is an upstream pro-inflammatory cytokine that is associated with the pathogenesis of autoimmune inflammatory diseases including rheumatoid arthritis (RA). Two polymorphisms in the upstream region exist in the MIF gene and are associated with RA susceptibility or severity in different populations. In this case-control study, we investigated whether MIF polymorphisms are associated with RA susceptibility or activity in a western Mexican population .The relationship of MIF levels with clinical features of disease also was assessed. Genotyping of the -794 CATT5-8 (rs5844572) and the -173 G>C (rs755622) polymorphisms was performed by PCR and PCR-RFLP respectively on 226 RA patients and 210 healthy subjects. Serum MIF levels were determined by ELISA. We found a significant association between the -794 CATT5-8 6,7 MIF genotype with RA. Moreover, we detected an association between the -794 CATT7 allele with early onset RA. The -794 CATT7 and -173(*)C alleles, which are in linkage disequilibrium, were associated with high disease activity on RA patients. A positive correlation between circulating MIF levels and C-reactive protein, erythrocyte sedimentation rate, rheumatoid factor, anti-citrullinated protein/peptides antibodies and TNFα was detected. MIF levels appear to be associated with disease progression rather than disease activity, which is distinct from the established relationship between disease activity and TNFα levels. In conclusion, the MIF gene and protein are associated with RA in a western Mexican population, with a main contribution onto early onset and early stages of disease.

Mechanism of the modulation of Kv4:KChIP-1 channels by external K+.

In response to a prolonged membrane depolarization, inactivation autoregulates the activity of voltage-gated ion channels. Slow inactivation involving a localized constriction of the selectivity filter (P/C-type mechanism) is prevalent in many voltage-gated K(+) channels of the Kv1 subfamily. However, the generalization of this mechanism to other Kv channel subfamilies has remained uncertain and controversial. In agreement with a "foot-in-the-door" mechanism and the presence of ion-ion interactions in the pore, elevated external K(+) slows the development of P/C-type inactivation and accelerates its recovery. In sharp contrast and resembling the regulation of the hippocampal A-type K(+) current, we found that Kv4.x channels associated with KChIP-1 (an auxiliary subunit) exhibit accelerated inactivation and unaffected recovery from inactivation when exposed to elevated external K(+). This regulation depends on the ability of a permeant ion to enter the selectivity filter (K(+) = Rb(+) = NH4(+) > Cs(+) > Na(+)); and the apparent equilibrium dissociation constant of a single regulatory site is 8 mM for K(+). By applying a robust quantitative global kinetic modeling approach to all macroscopic properties over a 210-mV range of membrane potentials, we determined that elevated external K(+) inhibits unstable closed states outside the main activation pathway and thereby promotes preferential closed-state inactivation. These results suggest the presence of a vestigial and unstable P/C-type mechanism of inactivation in Kv4 channels and strengthen the concept of novel mechanisms of closed-state inactivation. Regulation of Kv4 channel inactivation by hyperkalemia may help to explain the pathophysiology of electrolyte imbalances in excitable tissues.

Plasma intercellular adhesion molecule-1 and von Willebrand factor in primary graft dysfunction after lung transplantation.

Primary graft dysfunction (PGD), a form of acute lung injury occurring within 72 h following lung transplantation, is characterized by pulmonary edema and diffuse alveolar damage. We hypothesized that higher concentrations of intercellular adhesion molecule-1 (ICAM-1) and von Willebrand factor (vWF) would be associated with the occurrence of PGD. A total of 128 lung transplant recipients among 7 lung transplant centers were enrolled in a multicenter, prospective, cohort study. Blood specimens were collected preoperatively and at 6, 24, 48 and 72 h following lung transplantation. The primary outcome was Grade 3 PGD at 72 h after transplant. Logistic regression and generalized estimating equations (GEE) were used to analyze plasma ICAM-1 and vWF. At each postoperative timepoint, mean plasma ICAM-1 concentrations were higher for patients with PGD versus no PGD. The GEE contrast estimate for the association of plasma ICAM-1 with PGD was 107.5 ng/mL (95% CI 38.7, 176.3), p = 0.002. In the multivariate analyses, this finding was independent of all clinical variables except pulmonary artery pressures prior to transplant. There was no association between plasma vWF levels and PGD. We conclude that higher levels of plasma ICAM-1 are associated with PGD following lung transplantation.

Kv4 channels exhibit modulation of closed-state inactivation in inside-out patches.

The mechanisms of inactivation gating of the neuronal somatodendritic A-type K(+) current and the cardiac I(to) were investigated in Xenopus oocyte macropatches expressing Kv4.1 and Kv4.3 channels. Upon membrane patch excision (inside-out), Kv4.1 channels undergo time-dependent acceleration of macroscopic inactivation accompanied by a parallel partial current rundown. These changes are readily reversible by patch cramming, suggesting the influence of modulatory cytoplasmic factors. The consequences of these perturbations were investigated in detail to gain insights into the biophysical basis and mechanisms of inactivation gating. Accelerated inactivation at positive voltages (0 to +110 mV) is mainly the result of reducing the time constant of slow inactivation and the relative weight of the slow component of inactivation. Concomitantly, the time constants of closed-state inactivation at negative membrane potentials (-90 to -50 mV) are substantially decreased in inside-out patches. Deactivation is moderately accelerated, and recovery from inactivation and the peak G--V curve exhibit little or no change. In agreement with more favorable closed-state inactivation in inside-out patches, the steady-state inactivation curve exhibits a hyperpolarizing shift of approximately 10 mV. Closed-state inactivation was similarly enhanced in Kv4.3. An allosteric model that assumes significant closed-state inactivation at all relevant voltages can explain Kv4 inactivation gating and the modulatory changes.

The genotoxicity of 3-nitrobenzanthrone and the nitropyrene lactones in human lymphoblasts.

Polycyclic aromatic hydrocarbons (PAH) and nitrated polycyclic aromatic compounds (nitro-PAC) have been found to be mutagenic in bacterial and human cells as well as carcinogenic in rodents. In this investigation, the genotoxic effects of 3-nitrobenzanthrone (3NB) and a mixture of nitropyrene lactones (NPLs) were determined using forward mutation assays performed in two human B-lymphoblastoid cell lines, MCL-5 and h1A1v2, which are responsive to the nitro-PAC class of compounds. Mutagenicity of the compounds was determined at the heterozygous tk locus and the hemizygous hprt locus, thus, identifying both large-scale loss of heterozygosity (LOH) events as well as intragenic mutagenic events. Genotoxicity was also determined using the CREST modified micronucleus assay, which detects chromosomal loss and breakage events. Results indicate 3NB is an effective human cell mutagen, significantly inducing mutations at the tk and hprt loci in both cell lines, and inducing micronuclei in the h1A1v2 cell line. The NPL isomers are also mutagenic, inducing mutations at the two loci as well as micronuclei in both cell lines. Because of their mutagenic potencies and their presence in ambient air, further assessments should be made of human exposures to these nitro-PAC and the potential health risks involved.

Axial and angular correlations between colloidal particles in narrow cylindrical pores

In this work we present a study of the local structure of a model colloidal suspension highly confined inside a cylindrical pore. Such a study is based in Monte Carlo computer simulations, using the repulsive part of the Derjaguin-Landau-Verwey-Overbeek potential as the pair interaction between particles. The structural properties calculated here are the concentration profile n(rho), the axial pair correlation function g(z), and the axial-angular pair correlation function g(z,straight phi). The behavior of these quantities is analyzed as a function of the density of colloidal particles in the restricted space, and as a function of the size of the pore.

Potent inhibition of the aortic smooth muscle maxi-K channel by clinical doses of ethanol.

We investigated the effects of clinically relevant ethanol concentrations (5-20 mM) on the single-channel kinetics of bovine aortic smooth muscle maxi-K channels reconstituted in lipid bilayers (1:1 palmitoyl-oleoyl-phosphatidylethanolamine: palmitoyl-oleoyl-phosphatidylcholine). Ethanol at 10 and 20 mM decreased the channel open probability (P(o)) by 75 +/- 20.3% mainly by increasing the mean closed time (+82 to +960%, n = 7). In some instances, ethanol also decreased the mean open time (-40.8 +/- 22. 5%). The P(o)-voltage relation in the presence of 20 mM ethanol exhibited a rightward shift in the midpoint of voltage activation (DeltaV(1/2) congruent with 17 mV), a slightly steeper relationship (change in slope factor, Deltak, congruent with -2.5 mV), and a decreased maximum P(o) (from approximately 0.82 to approximately 0. 47). Interestingly, channels inhibited by ethanol at low Ca(2+) concentrations (2.5 microM) were very resistant to ethanol in the presence of increased Ca(2+) (>/= 20 microM). Alcohol consumption in clinically relevant amounts may alter the contribution of maxi-K channels to the regulation of arterial tone.

Bart syndrome: the congenital localized absence of skin may follow the lines of Blaschko. Report of six cases.

Three cutaneous manifestations are characteristic of Bart syndrome: congenital localized absence of skin (CLAS), mucocutaneous blistering, and nail abnormalities. Six cases of Bart syndrome are herein reported. Localized absence of skin is present at birth, particularly on the anterior aspects of the lower extremities and dorsa of the feet. Physical trauma in utero has been proposed as a mechanism to explain the denuded areas on the limbs. The recurrent, highly similar pattern of the congenital defect in regard to location and clinical appearance in our patients and in most of the reported cases strongly suggests that trauma is too simplistic an explanation. Because of the observed bilateral and symmetric distribution of denuded areas in an S-shaped broad band, their sharply demarcated borders, the involvement of the toe webs, and the frequent similar involvement of the soles, we suggest that congenital localized absence of skin in Bart syndrome may follow the lines of Blaschko.

General anesthetic action at an internal protein site involving the S4-S5 cytoplasmic loop of a neuronal K(+) channel.

The structural bases of general anesthetic action on a neuronal K(+) channel were investigated using the series of homologous 1-alkanols, electrophysiology, and mutational analysis. Domain swapping between dShaw2 (alkanol-sensitive) and hKv3.4 (alkanol-resistant) and site-directed mutagenesis demonstrated that a 13-amino acid cytoplasmic loop (S4-S5) determines the selective inhibition of native dShaw2 channels by 1-alkanols. The S4-S5 loop may contribute to a receptor for both 1-alkanols and the inactivation particle, because the enhanced 1-alkanol sensitivity of hKv3.4 channels hosting S4-S5 mutations correlates directly with disrupted channel inactivation. Evidence of a discrete protein site was also obtained from the analysis of the relationship between potency and alkyl chain length, which begins to level off after 1-hexanol. Rapid application to the cytoplasmic side of inside-out membrane patches shows that the interaction between dShaw2 channels and 1-alkanols equilibrates in <200 ms. By contrast, the equilibration time is >1000-fold slower when the drug is applied externally to outside-out membrane patches. The data strongly favor a mechanism of inhibition involving a discrete internal site for 1-alkanols in dShaw2 K(+) channels. A new working hypothesis proposes that 1-alkanols lock dShaw2 channels in their closed conformation by a direct interaction at a crevice formed by the S4-S5 loop.

Injection of Xenopus oocytes with mRNA from cultured neurons induces new currents and susceptibility to the damaging action of ruthenium red.

The hexacationic dye ruthenium red produce neuronal death in primary cultures. We injected messenger RNA (mRNA) from cultured neurons into Xenopus laevis oocytes to test whether this treatment can make oocytes sensitive to the damaging action of ruthenium red. Two-microelectrode voltage clamp and resting membrane potential were used to evaluate mRNA expression and to assess the effect of the dye on oocyte survival, when added to the medium or when injected into the cells, at 20, 50, or 100 microM concentrations. Injection of mRNA from cultured cortical or cerebellar granule neurons produced both new outward currents and membrane hyperpolarization. Exposure of mRNA-injected oocytes to extracellular ruthenium red for 24 h induced a remarkable depolarization, but no significant damage was observed. Injection of the dye into buffer-injected oocytes did not cause any change in membrane potential or cell survival, whereas in mRNA-injected oocytes an important depolarization was observed at 24 h after ruthenium red introduction, and 29% of the cells showed serious damage. The results suggest that oocytes become sensitive to intracellular ruthenium red toxicity because they express neuronal-specific proteins involved in cell death.

Inactivation gating of Kv4 potassium channels: molecular interactions involving the inner vestibule of the pore.

Kv4 channels represent the main class of brain A-type K+ channels that operate in the subthreshold range of membrane potentials (Serodio, P., E. Vega-Saenz de Miera, and B. Rudy. 1996. J. Neurophysiol. 75:2174- 2179), and their function depends critically on inactivation gating. A previous study suggested that the cytoplasmic NH2- and COOH-terminal domains of Kv4.1 channels act in concert to determine the fast phase of the complex time course of macroscopic inactivation (Jerng, H.H., and M. Covarrubias. 1997. Biophys. J. 72:163-174). To investigate the structural basis of slow inactivation gating of these channels, we examined internal residues that may affect the mutually exclusive relationship between inactivation and closed-state blockade by 4-aminopyridine (4-AP) (Campbell, D.L., Y. Qu, R.L. Rasmussen, and H.C. Strauss. 1993. J. Gen. Physiol. 101:603-626; Shieh, C.-C., and G.E. Kirsch. 1994. Biophys. J. 67:2316-2325). A double mutation V[404,406]I in the distal section of the S6 region of the protein drastically slowed channel inactivation and deactivation, and significantly reduced the blockade by 4-AP. In addition, recovery from inactivation was slightly faster, but the pore properties were not significantly affected. Consistent with a more stable open state and disrupted closed state inactivation, V[404,406]I also caused hyperpolarizing and depolarizing shifts of the peak conductance-voltage curve ( approximately 5 mV) and the prepulse inactivation curve (>10 mV), respectively. By contrast, the analogous mutations (V[556,558]I) in a K+ channel that undergoes N- and C-type inactivation (Kv1.4) did not affect macroscopic inactivation but dramatically slowed deactivation and recovery from inactivation, and eliminated open-channel blockade by 4-AP. Mutation of a Kv4-specific residue in the S4-S5 loop (C322S) of Kv4.1 also altered gating and 4-AP sensitivity in a manner that closely resembles the effects of V[404, 406]I. However, this mutant did not exhibit disrupted closed state inactivation. A kinetic model that assumes coupling between channel closing and inactivation at depolarized membrane potentials accounts for the results. We propose that components of the pore's internal vestibule control both closing and inactivation in Kv4 K+ channels.

Elejalde syndrome--a melanolysosomal neurocutaneous syndrome: clinical and morphological findings in 7 patients.

BACKGROUND: Silvery hair and severe dysfunction of the central nervous system (neuroectodermal melanolysosomal disease or Elejalde syndrome) characterize this rare autosomal recessive disease. Main clinical features include silver-leaden hair, bronze skin after sun exposure, and neurologic involvement (seizures, severe hypotonia, and mental retardation). Large granules of melanin unevenly distributed in the hair shaft are observed. Abnormal melanocytes and melanosomes and abnormal inclusion bodies in fibroblasts may be present. Differential diagnosis with Chédiak-Higashi syndrome and Griscelli syndrome must be done. OBSERVATIONS: We studied pediatric patients with silvery hair and profound neurologic dysfunction. Immune impairment was absent. Age of onset of neurologic signs ranged from 1 month to 11 years; the signs included severe muscular hypotonia, ocular alterations, and seizures. Mental retardation since the first months of life was noted in 4 cases. Psychomotor development was normal in 3 cases, but suddenly the patients presented with a regressive neurologic process. Four patients died between 6 months and 3 years after the onset of neurologic dysfunction. One patient showed characteristic ultrastructural findings of Elejalde syndrome. CONCLUSIONS: Elejalde syndrome is different from Chédiak-Higashi and Griscelli syndrome and is characterized by silvery hair and frequent occurrence of fatal neurologic alterations. Psychomotor impairment may have 2 forms of presentation: congenital or infantile. Although Elejalde syndrome and Griscelli syndrome are similar, the possibility that they are 2 different diseases, although probably allelic related, is suggested.

Surgical facial wounds: simple interrupted percutaneous suture versus running intradermal suture.

The purpose of this study is to compare the esthetics of scars resulting from small surgical facial wounds sutured either with simple interrupted percutaneous suture (SIPS) or with running intradermal suture (RIS). 93 small (0.6-1.9 cm) benign, facial new growths, mostly (86%) intradermal nevi were surgically removed. Forty-seven surgical wounds were sutured with SIPS and 46 with RIS. All surgical procedures were performed by the same dermatologic surgeon. For comparison, lesions were grouped in five facial areas. Other variables such as the age of the patient and type and size of lesions were similar in both groups. Evaluation of each scar was made blindly by two independent observers and by the patients. Judged by independent observers 90 days after surgery, excellent (45 %) to good (45%) results were obtained in similar proportion with either SIPS or RIS suturing in 90% of the patients. In the patients' self evaluation, excellent (85%) to good (14%) results were obtained in 99% of the cases. Suture marks and tracks present 30 days after surgery in 28% of scars sutured with SIPS disappeared 90 days after surgery. The esthetic results obtained by suturing small surgical facial wounds with SIPS or RIS were similarly good to excellent when observed 90 days after surgery. There was no advantage in using RIS over SIPS in the type of wounds described.

Control of K+ channel gating by protein phosphorylation: structural switches of the inactivation gate.

Fast N-type inactivation of voltage-dependent potassium (Kv) channels controls membrane excitability and signal propagation in central neurons and occurs by a 'ball-and-chain'-type mechanism. In this mechanism an N-terminal protein domain (inactivation gate) occludes the pore from the cytoplasmic side. In Kv3.4 channels, inactivation is not fixed but is dynamically regulated by protein phosphorylation. Phosphorylation of several identified serine residues on the inactivation gate leads to reduction or removal of fast inactivation. Here, we investigate the structure-function basis of this phospho-regulation with nuclear magnetic resonance (NMR) spectroscopy and patch-clamp recordings using synthetic inactivation domains (ID). The dephosphorylated ID exhibited compact structure and displayed high-affinity binding to its receptor. Phosphorylation of serine residues in the N- or C-terminal half of the ID resulted in a loss of overall structural stability. However, depending on the residue(s) phosphorylated, distinct structural elements remained stable. These structural changes correlate with the distinct changes in binding and unbinding kinetics underlying the reduced inactivation potency of phosphorylated IDs.

The use of retinoids in the pediatric patient.

Oral retinoids are molecules derived from vitamin A that represent one of the most important steps forward in dermatologic therapeutics in the present century. The treatment of acne, severe psoriasis, and severe disorders of keratinization, prevalent diseases in children and adolescents, have radically changed since the advent of oral retinoids. Like most highly-effective medications, oral retinoids also have important untoward effects. Specialists, and in particular, dermatologists and pediatricians should be prepared to maneuver the delicate balance between therapeutic efficacy and side effects in order to give the pediatric patient the maximum benefit with the lowest possible risk.

Receptor-coupled regulation of K+ channel N-type inactivation.

Phosphorylation of the inactivation gate of a K+ channel (Kv3.4) by protein kinase C (PKC) slows rapid N-type inactivation. To demonstrate that such an effect could occur under more physiological conditions, Kv3.4 and a metabotropic serotonin (5-HT) receptor were coexpressed in Xenopus oocytes. Application of 5-HT 10 microM to these oocytes produced two main effects: 1) Enhanced activity of endogenous Ca(++)-dependent Cl- channels; and 2) Kv3.4 currents exhibited significantly slower inactivation than the control currents (time constants at +50 mV: 7.1 +/- 0.6 ms and 14.7 +/- 3 ms, before and after 5-HT, respectively). These results are consistent with the presence of receptor-coupled activation of phospholipase C. 5-HT had little or no effect on Kv3.4 current kinetics when four N-terminal serines were mutated to alanine. Peak currents exhibited, however, a slow run-down. This study demonstrates that physiological activation of PKC may regulate K+ channel inactivation by a direct action.

Interactions between multiple phosphorylation sites in the inactivation particle of a K+ channel. Insights into the molecular mechanism of protein kinase C action.

Protein kinase C inhibits inactivation gating of Kv3.4 K+ channels, and at least two NH2-terminal serines (S15 and S21) appeared involved in this interaction (. Neuron. 13:1403-1412). Here we have investigated the molecular mechanism of this regulatory process. Site-directed mutagenesis (serine --> alanine) revealed two additional sites at S8 and S9. The mutation S9A inhibited the action of PKC by approximately 85%, whereas S8A, S15A, and S21A exhibited smaller reductions (41, 35, and 50%, respectively). In spite of the relatively large effects of individual S --> A mutations, simultaneous mutation of the four sites was necessary to completely abolish inhibition of inactivation by PKC. Accordingly, a peptide corresponding to the inactivation domain of Kv3.4 was phosphorylated by specific PKC isoforms, but the mutant peptide (S[8,9,15,21]A) was not. Substitutions of negatively charged aspartate (D) for serine at positions 8, 9, 15, and 21 closely mimicked the effect of phosphorylation on channel inactivation. S --> D mutations slowed the rate of inactivation and accelerated the rate of recovery from inactivation. Thus, the negative charge of the phosphoserines is an important incentive to inhibit inactivation. Consistent with this interpretation, the effects of S8D and S8E (E = Glu) were very similar, yet S8N (N = Asn) had little effect on the onset of inactivation but accelerated the recovery from inactivation. Interestingly, the effects of single S --> D mutations were unequal and the effects of combined mutations were greater than expected assuming a simple additive effect of the free energies that the single mutations contribute to impair inactivation. These observations demonstrate that the inactivation particle of Kv3.4 does not behave as a point charge and suggest that the NH2-terminal phosphoserines interact in a cooperative manner to disrupt inactivation. Inspection of the tertiary structure of the inactivation domain of Kv3.4 revealed the topography of the phosphorylation sites and possible interactions that can explain the action of PKC on inactivation gating.