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We have investigated the effects of vanadate (Vi) on force generation by, and shortening of, chemically skinned smooth muscle preparations from guinea-pig taenia coli at 22 degrees C. A method, using phosphatase inhibitors, was introduced to obtain stable, long-lasting contractions in thiophosphorylated preparations. Vi (10-1000 microM) dose-dependently inhibited active force, to about 20% of its maximum level. At a higher temperature (30 degrees C), the rate of inhibition was faster but the extent of inhibition was less. The rate of contraction following photolytic release of ATP to fibres in rigor was not affected by Vi (30 microM). The maximal shortening velocity (Vmax) was inhibited in a similar manner as active force by Vi (30 microM). In conclusion, the results suggest that Vi interacts with a force-generating actomyosin-ADP (AMADP) state reached after phosphate release. The rate of inhibition of smooth muscle contraction was markedly lower than in skeletal muscle, suggesting differences either in properties of the Vi-bound states or, more likely, in the concentration of AMADP states capable of binding Vi. This suggests that the long duty cycle in smooth muscle is not associated with a higher relative population of AMADP states reached immediately after Pi release, but rather by an increase in the population of subsequent force-generating cross-bridge states. The Vi-bound cross-bridges introduce an internal load to shortening, possibly acting in a similar manner as cross-bridge states introduced at low levels of activation.

BackgroundCalcium oxalate crystals, which are found in many organs of plants, have different morphological forms: as druses, prism, styloids, raphides and crystal sand. In this study, the distribution, type and specific location of calcium oxalate crystals in the leaves and stems of the eight species of poisonous plants and one species of nonpoisonous plant were investigated with light microscopy. During study special attention was given to the possible correlation between the presence and types of calcium oxalate crystals and toxic plant organs. The plants examined in this study were Hedera helix L. (Araliaceae), Aristolochia clematitis L. (Aristolochiaceae), Humulus lupulus L. (Cannabaceae), Saponaria officinalis L. (Caryophyllaceae), Chelidonium majus L. (Papaveraceae), Hypericum perforatum L. (Hypericaceae), Tribulus terrestris L. (Zygophyllaceae), Cynanchum acutum L. (Asclepiadaceae), and Nerium oleander L. (Apocynaceae).ResultsThree types of crystals: druses, prismatic crystals and crystal sands were observed. Druses were identified in the leaves and stems of six species of studied plants. In contrast to druses, crystal sands and prismatic crystals were rare. Prismatic crystals were observed in the leaf mesophlly cells of both Nerium oleander and Cynanchum acutum. However, crystal sands were observed only in the pith tissue of Humulus lupulus. On the other hand, leaves and stems of Chelidonium majus, Aristolochia clematitis and Hypericum perforatum were devoid of crystals.ConclusionThere is no absolute correlation between the presence and type of calcium oxalate crystals and toxic plant organs. However druse crystals may function as main irritant in toxic organs of the plants.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-55-32) contains supplementary material, which is available to authorized users.

a b s t r a c tRecent evidence suggests that non-muscle myosin IIB (NMIIB) contributes to smooth muscle contraction. This study was designed to determine the effects of NMIIB on the cross-bridge cycling rate. The cross-bridge cycling rate was investigated using sinusoidal analysis. Frequency analysis revealed two asymptotes in the Bode plot of the data; and the intersection of the asymptotes (corner frequency) was higher for the B +/À strain (8.73 ± 1.10 Hz vs 16.56 ± 1.26 Hz, P < 0.05), consistent with a higher overall cross-bridge cycling rate in heterozygous NMIIB KO (B +/À ) vs WT mice. These results demonstrate that because of their long duty cycle, NMIIB cross-bridges act as an internal load on smooth muscle myosin to decrease the overall cross-bridge cycling rate and muscle V max during force maintenance.

Stretching exercises are known for reduction of musculoskeletal stiffness and elongation of electromechanical delay (EMD). However, computing a change in stiffness by means of time delays, detected between onset of electromyographic (EMG), mechanomyographic (MMG) and force signals, can reveal changes in subcomponents (Δt EMG-MMG and Δt MMG-FORCE) of EMD after stretching. In our study, the effect of stretching was investigated while quadriceps femoris (QF) muscle performed isometric contractions. The EMG, MMG, and Force signals were recorded from rectus femoris (RF) and vastus medialis (VM) during five voluntarily isometric contractions at 15°, 30°, and 45° of knee flexion angle, while the leg was positioned on a custom-made device. Subjects in both intervention and control groups underwent same recording procedure before and after stretching. No difference between the baseline repeated contractions (before stretching) was ensured by ANOVA for repeated measures while a difference between PRE and POST was analyzed and concluded based on the effect size results. The EMD did not change; however, subcomponents (Δt EMG-MMG and Δt MMG-FORCE) showed differences within RF and VM muscles after stretching. The 30° knee flexion angle appears to be a position where isometric contraction intensity needs to be carefully monitored during rehabilitation period.