The delayed rectifier potassium conductance in the sarcolemma and the transverse tubular system membranes of mammalian skeletal muscle fibers.

A two-microelectrode voltage clamp and optical measurements of membrane potential changes at the transverse tubular system (TTS) were used to characterize delayed rectifier K currents (IK(V)) in murine muscle fibers stained with the potentiometric dye di-8-ANEPPS. In intact fibers, IK(V) displays the canonical hallmarks of K(V) channels: voltage-dependent delayed activation and decay in time. The voltage dependence of the peak conductance (gK(V)) was only accounted for by double Boltzmann fits, suggesting at least two channel contributions to IK(V). Osmotically treated fibers showed significant disconnection of the TTS and displayed smaller IK(V), but with similar voltage dependence and time decays to intact fibers. This suggests that inactivation may be responsible for most of the decay in IK(V) records. A two-channel model that faithfully simulates IK(V) records in osmotically treated fibers comprises a low threshold and steeply voltage-dependent channel (channel A), which contributes ∼31% of gK(V), and a more abundant high threshold channel (channel B), with shallower voltage dependence. Significant expression of the IK(V)1.4 and IK(V)3.4 channels was demonstrated by immunoblotting. Rectangular depolarizing pulses elicited step-like di-8-ANEPPS transients in intact fibers rendered electrically passive. In contrast, activation of IK(V) resulted in time- and voltage-dependent attenuations in optical transients that coincided in time with the peaks of IK(V) records. Normalized peak attenuations showed the same voltage dependence as peak IK(V) plots. A radial cable model including channels A and B and K diffusion in the TTS was used to simulate IK(V) and average TTS voltage changes. Model predictions and experimental data were compared to determine what fraction of gK(V) in the TTS accounted simultaneously for the electrical and optical data. Best predictions suggest that K(V) channels are approximately equally distributed in the sarcolemma and TTS membranes; under these conditions, >70% of IK(V) arises from the TTS

Recovery from acidosis is a robust trigger for loss of force in murine hypokalemic periodic paralysis.

Periodic paralysis is an ion channelopathy of skeletal muscle in which recurrent episodes of weakness or paralysis are caused by sustained depolarization of the resting potential and thus reduction of fiber excitability. Episodes are often triggered by environmental stresses, such as changes in extracellular K+, cooling, or exercise. Rest after vigorous exercise is the most common trigger for weakness in periodic paralysis, but the mechanism is unknown. Here, we use knock-in mutant mouse models of hypokalemic periodic paralysis (HypoKPP; NaV1.4-R669H or CaV1.1-R528H) and hyperkalemic periodic paralysis (HyperKPP; NaV1.4-M1592V) to investigate whether the coupling between pH and susceptibility to loss of muscle force is a possible contributor to exercise-induced weakness. In both mouse models, acidosis (pH 6.7 in 25% CO2) is mildly protective, but a return to pH 7.4 (5% CO2) unexpectedly elicits a robust loss of force in HypoKPP but not HyperKPP muscle. Prolonged exposure to low pH (tens of minutes) is required to cause susceptibility to post-acidosis loss of force, and the force decrement can be prevented by maneuvers that impede Cl- entry. Based on these data, we propose a mechanism for post-acidosis loss of force wherein the reduced Cl- conductance in acidosis leads to a slow accumulation of myoplasmic Cl- A rapid recovery of both pH and Cl- conductance, in the context of increased [Cl]in/[Cl]out, favors the anomalously depolarized state of the bistable resting potential in HypoKPP muscle, which reduces fiber excitability. This mechanism is consistent with the delayed onset of exercise-induced weakness that occurs with rest after vigorous activity

Trends in consumer sentiment and spending

In 2008, personal consumption expenditures represented 70% of gross domestic product, or total spending on final goods and services, according to U.S. Bureau of Economic Analysis data. This article analyzes consumer sentiment and spending data to uncover differences across income and education level groups.Personal Consumption Expenditures Price Index

Stac3 enhances expression of human CaV1.1 in Xenopus oocytes and reveals gating pore currents in HypoPP mutant channels.

Mutations of CaV1.1, the pore-forming subunit of the L-type Ca2+ channel in skeletal muscle, are an established cause of hypokalemic periodic paralysis (HypoPP). However, functional assessment of HypoPP mutant channels has been hampered by difficulties in achieving sufficient plasma membrane expression in cells that are not of muscle origin. In this study, we show that coexpression of Stac3 dramatically increases the expression of human CaV1.1 (plus α2-δ1b and β1a subunits) at the plasma membrane of Xenopus laevis oocytes. In voltage-clamp studies with the cut-open oocyte clamp, we observe ionic currents on the order of 1 μA and gating charge displacements of ∼0.5-1 nC. Importantly, this high expression level is sufficient to ascertain whether HypoPP mutant channels are leaky because of missense mutations at arginine residues in S4 segments of the voltage sensor domains. We show that R528H and R528G in S4 of domain II both support gating pore currents, but unlike other R/H HypoPP mutations, R528H does not conduct protons. Stac3-enhanced membrane expression of CaV1.1 in oocytes increases the throughput for functional studies of disease-associated mutations and is a new platform for investigating the voltage-dependent properties of CaV1.1 without the complexity of the transverse tubule network in skeletal muscle

A gap isolation method to investigate electrical and mechanical properties of fully contracting skeletal muscle fibers

We describe here a single-gap isolation method that allows the simultaneous measurement of electrical activity and tension output from fully contracting segments of frog skeletal muscle fibers. By using single pulses and pulse trains of varying frequency (5–100 Hz), records obtained for both electrical and mechanical fiber response demonstrate that the physiological properties of the fiber segments have been preserved. Action potentials could be recorded free of movement artifacts, even while segments were in fused tetani and developing maximum tensions of more than 600 kN/m2. Single current pulses evoked action potentials that averaged 144 +/- 16 mV (mean +/- SD, n = 8) in amplitude and twitches that averaged 285 +/- 66 kN/m2 and 55 +/- 5 ms (mean +/- SD, n = 20) in magnitude and time to peak, respectively. Trains of action potentials elicited patterns of tension development that exhibited summation, unfused tetani, and fused tetani in a frequency-dependent manner. The AC and DC electrical properties of the single grease gap were modeled with a simple Thévenin equivalent circuit, which satisfactorily predicted the experimental results. Our methodology is easily implemented and potentially applicable to any muscle preparation in which fiber segments with an intact end attached to a piece of tendon can be dissected

Confocal Imaging of Transmembrane Voltage by SEER of di-8-ANEPPS

Imaging, optical mapping, and optical multisite recording of transmembrane potential (Vm) are essential for studying excitable cells and systems. The naphthylstyryl voltage-sensitive dyes, including di-8-ANEPPS, shift both their fluorescence excitation and emission spectra upon changes in Vm. Accordingly, they have been used for monitoring Vm in nonratioing and both emission and excitation ratioing modes. Their changes in fluorescence are usually much less than 10% per 100 mV. Conventional ratioing increases sensitivity to between 3 and 15% per 100 mV. Low sensitivity limits the value of these dyes, especially when imaged with low light systems like confocal scanners. Here we demonstrate the improvement afforded by shifted excitation and emission ratioing (SEER) as applied to imaging membrane potential in flexor digitorum brevis muscle fibers of adult mice. SEER—the ratioing of two images of fluorescence, obtained with different excitation wavelengths in different emission bands—was implemented in two commercial confocal systems. A conventional pinhole scanner, affording optimal setting of emission bands but less than ideal excitation wavelengths, achieved a sensitivity of up to 27% per 100 mV, nearly doubling the value found by conventional ratioing of the same data. A better pair of excitation lights should increase the sensitivity further, to 35% per 100 mV. The maximum acquisition rate with this system was 1 kHz. A fast “slit scanner” increased the effective rate to 8 kHz, but sensitivity was lower. In its high-sensitivity implementation, the technique demonstrated progressive deterioration of action potentials upon fatiguing tetani induced by stimulation patterns at \u3e40 Hz, thereby identifying action potential decay as a contributor to fatigue onset. Using the fast implementation, we could image for the first time an action potential simultaneously at multiple locations along the t-tubule system. These images resolved the radially varying lag associated with propagation at a finite velocity

Molecular Genetics of FAM161A in North American Patients with Early-Onset Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a hereditary disease that leads to the progressive degeneration of retinal photoreceptor cells and to blindness. It is caused by mutations in several distinct genes, including the ciliary gene FAM161A, which is associated with a recessive form of this disorder. Recent investigations have revealed that defects in FAM161A represent a rather prevalent cause of hereditary blindness in Israel and the Palestinian territories, whereas they seem to be rarely present within patients from Germany. Genetic or clinical data are currently not available for other countries. In this work, we screened a cohort of patients with recessive RP from North America to determine the frequency of FAM161A mutations in this ethnically-mixed population and to assess the phenotype of positive cases. Out of 273 unrelated patients, only 3 subjects had defects in FAM161A. A fourth positive patient, the sister of one of these index cases, was also identified following pedigree analysis. They were all homozygous for the p.T452Sfx3 mutation, which was previously reported as a founder DNA variant in the Israeli and Palestinian populations. Analysis of cultured lymphoblasts from patients revealed that mutant FAM161A transcripts were actively degraded by nonsense-mediated mRNA decay. Electroretinographic testing showed 30 Hz cone flicker responses in the range of 0.10 to 0.60 microvolts in all cases at their first visit (age 12 to 23) (lower norm = 50 μV) and of 0.06 to 0.32 microvolts at their most recent examination (age 27 to 43), revealing an early-onset of this progressive disease. Our data indicate that mutations in FAM161A are responsible for 1% of recessive RP cases in North America, similar to the prevalence detected in Germany and unlike the data from Israel and the Palestinian territories. We also show that, at the molecular level, the disease is likely caused by FAM161A protein deficiency.Version of Recor

Efectos del cloruro de cloro colina y el paclobutrazol sobre el crecimiento de plantas y la calidad de raíces tuberosas de mandioca (Manihot esculenta Crantz cv. Rocha)

The effects of chlorocholine chloride (CCC) and paclobutrazol (PBZ) foliar application on shoot and root parameters of cassava field-grown plants were studied (0, 45 and 90 mg active ingredient per plant). CCC and PBZ reduced total plant and first branch height, aerial fresh mass and tuberous root number. PBZ delayed branching and significantly decreased tuberous root fresh mass, while CCC caused no modifications in these parameters. In addition, CCC and PBZ treatments did not modify tuberous root diameter, while PBZ reduced tuberous root length significantly. Starch content was increased by both growth regulators at the lower dose, whereas dry matter content was increased only by CCC. In conclusion, CCC suppresses excessive vegetative growth, favours quality attributes and does not alter yield, hence improving harvest index. Although PBZ at a low dose increases the starch content and harvest index, its effects on other parameters are undesirable.Fil: Medina, Ricardo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Burgos, A.. Universidad Nacional del Nordeste; ArgentinaFil: Difranco, V.. Universidad Nacional del Nordeste; ArgentinaFil: Mroginski, Luis Amado. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Cenóz, P.. Universidad Nacional del Nordeste; Argentin

Spatial and temporal trends of dissolved nitrous oxide in the Lamprey River Watershed and controls on the end-products of denitrification

An understanding of the controls on the production of the greenhouse gas N2O is important to assess the atmospheric contribution of N2O from freshwater streams. Concentration and percent saturation of dissolved N2O were measured from March 2008 to February 2009 and were used as to measure the potential for streams in the Lamprey River Watershed to lose N2O to the atmosphere. Almost all streams were oversaturated most of the year, and though field concentrations of dissolved N2O did show trends with stream chemistry, it is possible that N2O is not only being produced within the streams themselves, but is entering the streams via groundwater and surface runoff. A controlled laboratory experiment was also conducted to determine controls on N2O and N2O production from denitrification. These controls were much more obvious than in the field study, suggesting that laboratory experiments may misrepresent field conditions

Williams, John, Oral history interview

Professor of English (1965 - 1998). Topics include: Raymond College, its community and style of teaching; demise of Raymond Endowment; transition to the College of Pacific English Department; design of the Mentor Program; interactions with the Regents.https://scholarlycommons.pacific.edu/esohc/1121/thumbnail.jp