Riparian land-use and rehabilitation: impact on organic matter input and soil respiration.

Rehabilitated riparian zones in agricultural landscapes enhance environmental integrity and provide environmental services such as carbon (C) sequestration. This study quantified differences in organic matter input, soil biochemical characteristics, and soil respiration in a 25-year-old rehabilitated (RH), grass (GRS), and undisturbed natural forest (UNF) riparian zone. Input from herbaceous vegetation was significantly greater (P < 0.05) in the GRS riparian zone, whereas autumnal litterfall was significantly greater (P < 0.05) in the RH riparian zone. Soil bulk density was significantly greater (P < 0.05) in the RH riparian zone, but its soil chemical characteristics were significantly lower. Soil respiration rates were lowest (P < 0.05) in the UNF (106 C m(-2) h(-1)), followed by the RH (169 mg C m(-2) h(-1)) and GRS (194 C m(-2) h(-1)) riparian zones. Soil respiration rates were significantly different (P < 0.05) among seasons, and were significantly correlated with soil moisture (P < 0.05) and soil temperature (P < 0.05) in all riparian zones. Soil potential microbial activity indicated a significantly different (P < 0.05) response of the microbial metabolic diversity in the RH compared to the GRS and UNF riparian zones, and principle component analysis showed a distinct difference in microbial activity among the riparian land-use systems. Rehabilitating degraded riparian zones with trees rather than GRS is a more effective approach to the long-term mitigation of CO2. Therefore, the protection of existing natural/undisturbed riparian forests in agricultural landscapes is equally important as their rehabilitation with trees, given their higher levels of soil organic C and lower soil respiration rates.

Incidence of occult cleft palate on prenatal magnetic resonance images obtained for non-cleft indications.

Prenatal diagnosis of craniofacial anomalies has improved family education and preparedness. Isolated cleft palate, however, remains difficult to identify sonographically. The aim of this study was to investigate the rate of incidental cleft palate identified on fetal magnetic resonance imaging (MRI) following the ultrasound detection of non-cleft abnormalities. This was a retrospective study of pregnant women who had fetal MRI performed between 2003 and 2017. To be included, the woman had to have been referred for fetal imaging for a non-cleft indication, with subsequent identification of an isolated cleft palate on MRI. Fetuses with a postnatal diagnosis of Robin sequence were excluded. The study sample included 30 women. Mean gestational age at MRI was 24 weeks 4 days± 38 days. Most referrals (76.7%) were for non-cleft craniofacial anomalies, of which micrognathia was the most common (63.3%). The annual incidence of occult cleft palate diagnosis was 0.4%, and a genetic syndrome was suspected based on imaging findings in 76.7%. Although rare, isolated cleft palate found incidentally on fetal imaging led to concern for a genetic syndrome in a high percentage of cases. This suggests that early referral for fetal MRI may provide critical information when sonographic fetal anomalies have been identified.

Early weight gain in infants with Robin sequence after mandibular distraction.

This retrospective cohort study was performed to assess weight gain in infants with Robin sequence (RS) treated by mandibular distraction osteogenesis (MDO). The primary outcome variable was average daily weight gain for the following time periods: (1) birth to MDO (T1), (2) MDO to distractor removal (T2), (3) distractor removal to 6 months later (T3), and (4) 6 months to 12 months following distractor removal (T4). Published growth curves were used for comparison. Differences were assessed using the Wilcoxon matched-pairs signed rank test. Twenty-two infants were included in the study. During T1, the infants had 9.47 ± 12.61 g/day less weight gain than expected (P = 0.001). However, for T2, T3, and T4, the infants demonstrated 3.48 ± 6.17 g/day (P = 0.028), 2.19 ± 4.47 g/day (P = 0.030), and 1.83 ± 3.25 g/day (P = 0.028) more weight gain than expected. Feeding tube use resulted in improved weight gain during T1 (P < 0.001), but was associated with poorer weight gain in T3 (P = 0.003) and T4 (P = 0.001). In conclusion, infants with RS treated by MDO demonstrated poorer weight gain relative to their peers between birth and the MDO operation. However, from the MDO procedure to 12 months post-distractor removal, infants who had MDO showed faster weight gain than their age-matched peers.

Mechanism of insulin-induced paralysis of muscles from potassium-depleted rats.

Zinc-free insulin elicited a reduction in the potassium conductance of muscle fibers from potassium-depleted muscle, which led to depolarization, blockage of action-poteintial mechanism, and paralysis. These changes are proposed as the mechanism of insulin-induced paralysis in patients with hypokalemic periodic paralysis. A similar effect by concanavalin a suggests that the effect may be mediated through the insulin receptors.

Muscle activation: effects of small length changes on calcium release in single fibers.

In single muscle fibers, small (1 percent) changes of length have a marked effect of both the calcium activation and the tension elicited by a constant current stimulus. The decrease in tension with shortening is accounted for almost entirely by a decrease in calcium release, rather than by changes in mechanical factors, such as filament geometry.

Hysteresis in the force-calcium relation in muscle.

Calcium ions activate muscle contraction. The mechanism depends on the calcium sensitivity of the proteins that regulate contraction. Evidence is presented for the reverse phenomenon, where contraction modulates calcium sensitivity. Increasing the force level increased calcium sensitivity in intact fibers showing that the relation between force and calcium is not unique. A particular calcium concentration can maintain a higher force level than it can create. The results were confirmed in skinned fiber experiments. Transient reduction of the force led to a transient reduction in calcium binding, suggesting a simple mechanism for the hysteresis.

Spatial and Temporal Variation in Soil Nitrous Oxide Emissions from a Rehabilitated and Undisturbed Riparian Forest.

Riparian zones enhance water quality and provide wildlife habitat, but high nutrient input in agricultural landscapes causes nitrous oxide (NO) emissions, potentially negating their benefits of C sequestration. The objectives of this study were to quantify spatiotemporal NO emissions in a rehabilitated and undisturbed natural riparian forest. We also determined soil and vegetation characteristics, and their role in driving spatiotemporal NO emissions. Mean NO-N emissions were not significantly ( < 0.05) different between rehabilitated (7.62 µg m h) and undisturbed (5.93 µg m h) riparian forests. The greatest ( < 0.05) NO-N emissions in both riparian forests were observed during the summer. Soil moisture, temperature, and N were significantly correlated to NO-N emissions. Our results show that soil and vegetation characteristics varied between the two riparian forests, but differences in NO-N emissions were negligible. We also found that NO emissions were influenced by soil characteristics and seasonality, rather than vegetation characteristics or spatial position.

Partial purification of the sodium- and potassium-coupled L-glutamate transport glycoprotein from rat brain.

The sodium- and potassium-coupled L-glutamate transporter from rat brain has been solubilized with cholate and 10-20-fold purified using Wheat Germ Agglutinin-Sepharose 4B. Transport activity--as determined upon reconstitution of the fraction into liposomes--was retained on the column and eluted by N-acetylglucosamine. When the glycoprotein fraction was depleted of the N-acetylglucosamine and applied to a second round of lectin-chromatography, the L-glutamate transport activity was retained and again could be eluted by the sugar. The transporter activity reconstituted from the glycoprotein fraction exhibited the same features as that in synaptic plasma membranes, including electrogenicity, an absolute dependence on external sodium and internal potassium, affinity and stereospecificity. Furthermore, efflux and exchange properties of the reconstituted preparation were also unchanged by the solubilisation and lectin-chromatography. These observations indicate that the sodium- and potassium-coupled L-glutamate transporter is a glycoprotein and is predominantly reconstituted in the 'right-side-out' conformation.

Extra calcium on shortening in barnacle muscle. Is the decrease in calcium binding related to decreased cross-bridge attachment, force, or length?

Barnacle single muscle fibers were microinjected with the calcium-specific photoprotein aequorin. We have previously shown (Ridgway, E. B., and A. M. Gordon, 1984, Journal of General Physiology, 83:75-104) that when barnacle fibers are stimulated under voltage clamp and length control and allowed to shorten during the declining phase of the calcium transient, extra myoplasmic calcium is observed. The time course of the extra calcium for shortening steps at different times during the calcium transient is intermediate between those of free calcium and muscle force. Furthermore, the amplitude increases with an increased stimulus, calcium transient, and force. Therefore, the extra calcium probably comes from the activating sites on the myofilaments, possibly as a result of changes in calcium binding by the activating sites. The change in calcium binding may be due, in turn, to the change in muscle length and/or muscle force and/or cross-bridge attachment per se. In the present article, we show that the amount of the extra calcium depends on the initial muscle length, declining at shorter lengths. This suggests length-dependent calcium binding. The relation between initial length and extra calcium, however, parallels that between initial length and peak active force. The ratio of extra calcium to active force is therefore virtually independent of initial length. These data do not distinguish between a direct effect of length on calcium binding and an indirect effect owing to changes in cross-bridge attachment and force through some geometrical factor. The amount of extra calcium increases with the size of the shortening step, tending toward saturation for steps of greater than or equal to 10%. This experiment suggests that calcium binding depends on muscle force or cross-bridge attachment, not just length (if at all). There is much less extra calcium seen with shortening steps at high force when the high force results from stretch of the active muscle than when it results from increased stimulation of muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Force and stiffness in glycerinated rabbit psoas fibers. Effects of calcium and elevated phosphate.

Force (F) and stiffness (K) were measured in glycerinated psoas fibers at various calcium levels with 0, 10, 20, and 30 mM orthophosphate (Pi) added to the bathing solutions. The concentrations of bathing solution constituents were as follows: 110 mM potassium, 40 mM sodium, 4 mM MgATP, 10 mM total EGTA, and variable amounts of MOPS (pH buffer). The pH was 7.0, the ionic strength was 200 mM, and the temperature was 10 degrees C. Calcium levels were established by adding various amounts of CaCl2. All solutions contained 4% Dextran T-500. Fiber K was measured by imposing sinusoidal length changes (0.03-0.1%) at 1 kHz and by applying rapid steps in length and measuring the resulting F changes. At all [Pi] tested, K was more sensitive to calcium than F. Elevating bathing solution [Pi] caused a decrease in the calcium sensitivity of both F and K, while the slopes of F-calcium and K-calcium relations increased. In maximally activating calcium, raising [Pi] caused a continuous decrease in F over the range tested, while from very low to 10 mM Pi K remained constant. Above 10 mM Pi K declined, but to a lesser extent than did F. The results suggest that under our experimental conditions strongly attached crossbridges can exist in both force-producing and non-force-producing states, and that the relative population of these states may be calcium dependent.

Length-dependent electromechanical coupling in single muscle fibers.

In single muscle fibers from the giant barnacle, a small decrease in muscle length decreases both the calcium activation and the peak isometric tension produced by a constant current stimulus. The effect is most pronounced if the length change immediately precedes the stimulation. In some cases, the decrease in tension with shortening can be accounted for almost entirely by a decrease in calcium release rather than changes in mechanical factors such as filament geometry. During the constant current stimulation the muscle membrane becomes more depolarized at longer muscle lengths than at the shorter muscle lengths. Under voltage clamp conditions, when the membrane potential is kept constant during stimulation, there is little length dependence of calcium release. Thus, the effect of length on calcium release is mediated through a change in membrane properties, rather than an effect on a subsequent step in excitation-contraction coupling. Stretch causes the unstimulated fiber membrane to depolarize by about l mV while release causes the fiber membrane to hyperpolarize by about the same amount. The process causing this change in potential has an equilibrium potential nearly 10 mV hyperpolarized from the resting level. This change in resting membrane potential with length may account for the length dependence of calcium release.

Muscle calcium transient. Effect of post-stimulus length changes in single fibers.

We examined the effects of post-stimulus length changes on voltage-clamped, aequorin-injected single muscle fibers from the barnacle Balanus nubilus. Extra light (extra calcium) is seen when the fiber is allowed to shorten (a small percentage) during the declining phase of the calcium transient. The opposite is observed when the fiber is stretched. Increasing the extent of shortening increases the amount of extra calcium, as does decreasing the temperature. The extra calcium probably comes from the myofilaments and not from the sarcoplasmic reticulum because (a) there is a strong correlation between the extra calcium and the level of activation; (b) there is a strong correlation between the extra calcium and the amount of force redeveloped after a length change; and (c) the time course of the appearance of the extra calcium is intermediate between that of the free calcium concentration and that of force. We suggest (a) that the calcium binding to the activating myofibrillar proteins is sensitive to muscle length or muscle force, and (b) that there is a pool of bound calcium (activating calcium) that waxes and wanes with a time course intermediate between the free calcium concentration and force.

Some effects of hypertonic solutions on contraction and excitation-contraction coupling in frog skeletal muscles.

In frog fast skeletal muscle, we find a decline of twitch, tetanus, and maximum K and caffeine contracture tensions as tonicity of the bathing solution is increased. The decline of tension independent of the method of producing contraction indicates that the major effect of hypertonicity is directly on contractile tension probably because of the increased internal ionic strength. However, there is some apparent disruption of excitation-contraction (E-C) coupling in solutions made three times the normal tonicity (3T solutions) since: (a) in 3T solutions tetanic and K contracture tensions decline to zero from a value near the average maximum caffeine contracture tension at this tonicity (10% of 1T tetanic tension). At this time, caffeine contractures of 10% of 1T tetanic tension can be elicited; (b) once the K contracture tension has declined, elevated [Ca(++)](o), 19.8 mM, restores K contracture tension to 13% of 1T tetanic tension. This probable disruption is not caused by changes in mechanical threshold since in 2T solutions the mechanical threshold is shifted by 12 mv in the hyperpolarizing direction. This is consistent with neutralization of fixed negative charges on the inside of the membrane. The repriming curve is also shifted in the hyperpolarizing direction in 2T solutions. Shifts of the repriming curve coupled with membrane depolarizations in 3T solutions (about 20 mv) may produce loss of repriming ability at the resting potential and disruption of E-C coupling.

Stretch of active muscle during the declining phase of the calcium transient produces biphasic changes in calcium binding to the activating sites.

In voltage-clamped barnacle single muscle fibers, muscle shortening during the declining phase of the calcium transient increases myoplasmic calcium. This extra calcium is probably released from the activating sites by a change in affinity when cross-bridges break (Gordon, A. M., and E. B. Ridgway, 1987. J. Gen. Physiol. 90:321-340). Stretching the muscle at similar times causes a more complex response, a rapid increase in intracellular calcium followed by a transient decrease. The amplitudes of both phases increase with the rate and amplitude of stretch. The rapid increase, however, appears only when the muscle is stretched more than approximately 0.4%. This is above the length change that produces the breakpoint in the force record during a ramp stretch. This positive phase in response to large stretches is similar to that seen on equivalent shortening at the same point in the contraction. For stretches at different times during the calcium transient, the peak amplitude of the positive phase has a time course that is delayed relative to the calcium transient, while the peak decrease during the negative phase has an earlier time course that is more similar to the calcium transient. The amplitudes of both phases increase with increasing strength of stimulation and consequent force. When the initial muscle the active force. A large decrease in length (which drops the active force to zero) decreases the extra calcium seen on a subsequent restretch. After such a shortening step, the extra calcium on stretch recovers (50 ms half time) toward the control level with the same time course as the redeveloped force. Conversely, stretching an active fiber decreases the extra calcium on a subsequent shortening step that is imposed shortly afterward. Enhanced calcium binding due to increased length alone cannot explain our data. We hypothesize that the calcium affinity of the activating sites increases with cross-bridge attachment and further with cross-bridge strain. This accounts for the biphasic response to stretch as follows: cross-bridges detached by stretch first decrease calcium affinity, then upon reattachment increase calcium affinity due to the strained configuration brought on by the stretch. The experiments suggest that cross-bridge attachment and strain can modify calcium binding to the activating sites in intact muscle.

Muscle force and stiffness during activation and relaxation. Implications for the actomyosin ATPase.

Isolated skinned frog skeletal muscle fibers were activated (increasing [Ca2+]) and then relaxed (decreasing [Ca2+]) with solution changes, and muscle force and stiffness were recorded during the steady state. To investigate the actomyosin cycle, the biochemical species were changed (lowering [MgATP] and elevating [H2PO4-]) to populate different states in the actomyosin ATPase cycle. In solutions with 200 microM [MgATP], compared with physiological [MgATP], the slope of the plot of relative steady state muscle force vs. stiffness was decreased. At low [MgATP], cross-bridge dissociation from actin should be reduced, increasing the population of the last cross-bridge state before dissociation. These data imply that the last cross-bridge state before dissociation could be an attached low-force-producing or non-force-producing state. In solutions with 10 mM total Pi, compared to normal levels of MgATP, the maximally activated muscle force was reduced more than muscle stiffness, and the slope of the plot of relative steady state muscle force vs. stiffness was reduced. Assuming that in elevated Pi, Pi release from the cross-bridge is reversed, the state(s) before Pi release would be populated. These data are consistent with the conclusion that the cross-bridges are strongly bound to actin before Pi release. In addition, if Ca2+ activates the ATPase by allowing for the strong attachment of the myosin to actin in an A.M.ADP.Pi state, it could do so before Pi release. The calcium sensitivity of muscle force and stiffness in solutions with 4 mM [MgATP] was bracketed by that measured in solutions with 200 microM [MgATP], where muscle force and stiffness were more sensitive to calcium, and 10 mM total Pi, where muscle force and stiffness were less sensitive to calcium. The changes in calcium sensitivity were explained using a model in which force-producing and rigor cross-bridges can affect Ca2+ binding or promote the attachment of other cross-bridges to alter calcium sensitivity.

Tension in skinned frog muscle fibers in solutions of varying ionic strength and neutral salt composition.

The maximal calcium-activated isometric tension produced by a skinned frog single muscle fiber falls off as the ionic strength of the solution bathing this fiber is elevated declining to zero near 0.5 M as the ionic strength is varied using KCl. When other neutral salts are used, the tension always declines at high ionic strength, but there is some difference between the various neutral salts used. The anions and cations can be ordered in terms of their ability to inhibit the maximal calcium-activated tension. The order of increasing inhibition of tension (decreasing tension) at high ionic strength for anions is propionate(-) approximately SO(4) (--) < Cl(-) < Br(-). The order of increasing inhibition of calcium-activated tension for cations is K(+) approximately Na(+) approximately TMA(+) < TEA(+) < TPrA(+) < TBuA(+). The decline of maximal calcium-activated isometric tension with elevated salt concentration (ionic strength) can quantitatively explain the decline of isometric tetanic tension of a frog muscle fiber bathed in a hypertonic solution if one assumes that the internal ionic strength of a muscle fiber in normal Ringer's solution is 0.14-0.17 M. There is an increase in the base-line tension of a skinned muscle fiber bathed in a relaxing solution (no added calcium and 3 mM EGTA) of low ionic strength. This tension, which has no correlate in the intact fiber in hypotonic solutions, appears to be a noncalcium-activated tension and correlates more with a declining ionic strength than with small changes in [MgATP], [Mg], pH buffer, or [EGTA]. It is dependent upon the specific neutral salts used with cations being ordered in increasing inhibition of this noncalcium-activated tension (decreasing tension) as TPrA(+) < TMA(+) < K(+) approximately Na(+). Measurements of potentials inside these skinned muscle fibers bathed in relaxing solutions produced occasional small positive values (<6 mV) which were not significantly different from zero.

Nutritional status of Cuban refugees: a field study on the health and nutriture of refugees processed at Opa Locka, Florida.

A field study was conducted to evaluate the nutritional status of newly arrived Cuban refugees. The protocol consisted of socioeconomic, clinical, anthropometric, laboratory, and dietary investigations. A total of 138 refugees was studied at Opa Locka, Fl. The results revealed that 25% of children suffered from malnutrition mostly of the first degree. Second degree malnutrition was rare and cases of third degree malnutrition or infantile kwashiorkor were not found. Obesity was found in 17% of women. Of adults 25% had significantly low adipose tissue stores. Lean body mass was estimated by anthropometry and found to be adequate in 88% of adults. Fifteen percent of adults and 12% of children had anemia. The foods most frequently consumed by the refugees in Cuba were bread, eggs, rice, and garbanzo (chick peas). Fruits and vegetables were not consumed in Cuba daily by the majority of the refugees.

Alteration of skeletal muscle cellular structures by potassium depletion.

After rats had been fed a low-potassium diet for 4 to 8 weeks, skeletal muscle showed ultrastructural changes involving membranous organelles. Mitochondria were often swollen, condensed, or disintegrated. The transverse tubules were disoriented, focally dilated, and tortuous. The sarcoplasmic reticulum showed various degrees of dilatation. Vacuoles of different sizes occurred frequently. Whirls of membranes were closely associated with any of the membranous organelles, especially near an orifice of a transverse tubule. Supplementation of potassium reversed these changes. These findings are very similar to those in patients with hypokalemic periodic paralysis. The vacuolar myopathy in these patients may be secondary to the electrolyte alteration in skeletal muscles, and the chronic weakness of some patients may be due to excitation-contraction uncoupling as a result of the involvement of sarcotubular systems.

Objective assessment of progression in Huntington's disease: a 3-year follow-up study.

Objective measures to assess progression of Huntington's disease (HD) are desirable. The authors have previously found that patients with HD with higher Unified Huntington's Disease Rating Scale (UHDRS) motor scores exhibited higher variability of isometric grip forces while grasping an object. Therefore, the authors assessed grip force variability during this task in 10 HD patients with a 3-year follow-up. Grip force variability increased in all patients at the follow-up. Thus, grip force variability during grasping might be an objective and quantitative measure to assess motor deficits associated with the progression of HD.