A two-staged approach offers acceptable results for the treatment of severe pilon fractures. These results compare favorably with those of primary open reduction and of internal fixation and external fixation techniques. The major advantages include limited soft tissue complications and improved articular reconstruction.

BackgroundHuman respiratory epithelia function in airway mucociliary clearance and barrier function and have recently been implicated in sensory functions.ObjectiveWe investigated a link between chronic obstructive pulmonary disease (COPD) pathogenesis and molecular mechanisms underlying Ca2+ influx into human airway epithelia elicited by diesel exhaust particles (DEP).Methods and ResultsUsing primary cultures of human respiratory epithelial (HRE) cells, we determined that these cells possess proteolytic signaling machinery, whereby proteinase-activated receptor-2 (PAR-2) activates Ca2+-permeable TRPV4, which leads to activation of human respiratory disease–enhancing matrix metalloproteinase-1 (MMP-1), a signaling cascade initiated by diesel exhaust particles (DEP), a globally relevant air pollutant. Moreover, we observed ciliary expression of PAR-2, TRPV4, and phospholipase-Cβ3 in human airway epithelia and their DEP-enhanced protein–protein complex formation. We also found that the chronic obstructive pulmonary disease (COPD)–predisposing TRPV4P19S variant enhances Ca2+ influx and MMP 1 activation, providing mechanistic linkage between man-made air pollution and human airway disease.ConclusionDEP evoked protracted Ca2+ influx via TRPV4, enhanced by the COPD-predisposing human genetic polymorphism TRPV4P19S. This mechanism reprograms maladaptive inflammatory and extracellular-matrix–remodeling responses in human airways. The novel concept of air pollution–responsive ciliary signal transduction from PAR-2 to TRPV4 in human respiratory epithelia will accelerate rationally targeted therapies, possibly via the inhalatory route.

son. Denervation produces different single fiber phenotypes in fast-and slow-twitch hindlimb muscles of the rat. Am J Physiol Cell Physiol 291: C518 -C528, 2006. First published April 12, 2006 doi:10.1152/ajpcell.00013.2006.-Using a single, mechanically skinned fiber approach, we tested the hypothesis that denervation (0 to 50 days) of skeletal muscles that do not overlap in fiber type composition [extensor digitorum longus (EDL) and soleus (SOL) muscles of Long-Evans hooded rats] leads to development of different fiber phenotypes. Denervation (50 day) was accompanied by 1) a marked increase in the proportion of hybrid IIB/D fibers (EDL) and I/IIA fibers (SOL) from 30% to Ͼ75% in both muscles, and a corresponding decrease in the proportion of pure fibers expressing only one myosin heavy chain (MHC) isoform; 2) complex muscle-and fiber-type specific changes in sarcoplasmic reticulum Ca 2ϩ -loading level at physiological pCa ϳ7.1, with EDL fibers displaying more consistent changes than SOL fibers; 3) decrease by ϳ50% in specific force of all fiber types; 4) decrease in sensitivity to Ca 2ϩ , particularly for SOL fibers (by ϳ40%); 5) decrease in the maximum steepness of the force-pCa curves, particularly for the hybrid I/IIA SOL fibers (by ϳ35%); and 6) increased occurrence of biphasic behavior with respect to Sr 2ϩ activation in SOL fibers, indicating the presence of both slow and fast troponin C isoforms. No fiber types common to the two muscles were detected at any time points (day 7, 21, and 50) after denervation. The results provide strong evidence that not only neural factors, but also the intrinsic properties of a muscle fiber, influence the structural and functional properties of a particular muscle cell and explain important functional changes induced by denervation at both whole muscle and single cell levels. mechanically skinned fibers; myosin heavy chain isoforms; lineage; sarcoplasmic reticulum; Ca 2ϩ and Sr 2ϩ sensitivity; Long-Evans hooded rat MAMMALIAN SKELETAL MUSCLE fibers display a broad spectrum of structural and functional characteristics determined by the complement of homologous, but not identical, molecular structures involved in the excitation-contraction-relaxation cycle (33,34,41). Cross-innervation (4, 6), denervation (16,17,26,28,37), and chronic low-frequency stimulation (7,20,33,34) experiments have produced compelling evidence that the pattern of neural stimulation plays a crucial role in determining the functional and/or structural properties of skeletal muscle (38). However, neural control of fiber phenotype does not extend to the entire complement of cellular structures responsible for muscle fiber function, as demonstrated by crossinnervation studies. For example, when the extensor digitorum longus (EDL) muscle of the rat, a typically fast-twitch muscle, was cross-innervated by the nerve of the soleus (SOL) muscle, a typically slow-twitch muscle, the twitch time course of the cross-innervated muscle remained considerably faster than the twitch of the typical SOL muscle, even 16 ...

Intact rat ventricular trabeculae were injected with the salt form of fura 2, and the fura 2 ratio signal (R) was used to report intracellular Ca2+ concentration ([Ca2+]i). The fixed end relaxation phase of a twitch is associated with a slowing of the decay of the R signal, or even a reversal, to form a distinct bump, indicating a transient rise in [Ca2+]i. The bump is most prominent at 30°C, and motion artifact is not its cause. Increasing doses of 2,3-butanedione monoxime caused progressive attenuation of the twitch and bump. Increasing the bathing Ca2+ concentration potentiated the twitch and enhanced the bump. Imposed muscle shortening during relaxation caused a much quicker force decline, and this led to the appearance of a much more prominent associated bump. The amplitude of the bump depends on the amplitude of twitch force and the rate of relaxation. These findings can be explained, as in skeletal muscle, by making cross-bridge attachment and Ca2+ binding to troponin C strongly cooperative; therefore, the bump during fast relaxation is produced by a reversal of this cooperativity, leading to rapid dissociation of Ca2+ from troponin C into the myoplasm.

In this study, we investigated whether the previously established differences between fast- and slow-twitch single skeletal muscle fibers of the rat, in terms of myosin heavy chain (MHC) isoform composition and contractile function, are also detectable in excitation-contraction (E-C) coupling. We compared the contractile responsiveness of electrophoretically typed, mechanically skinned single fibers from the soleus (Sol), the extensor digitorum longus (EDL), and the white region of the sternomastoid (SM) muscle to t-system depolarization-induced activation. The quantitative parameters assessed were the amplitude of the maximum depolarization-induced force response (DIFR(max); normalized to the maximum Ca(2+)-activated force in that fiber) and the number of responses elicited until the force declined by 75% of DIFR(max) (R-D(75%)). The mean DIFR(max) values for type IIB EDL and type IIB SM fibers were not statistically different, and both were greater than the mean DIFR(max) for type I Sol fibers. The mean R-D(75%) for type IIB EDL fibers was greater than that for type I Sol fibers as well as type IIB SM fibers. These data suggest that E-C coupling characteristics of mechanically skinned rat single muscle fibers are related to MHC-based fiber type and the muscle of origin.

Many models have been developed to account for stimulus-evoked [Ca2+] responses, but few address how responses elicited in specific cell types are defined by the Ca2+ transport and buffering systems that operate in the same cells. In this study, we extend previous modeling studies by linking the time course of stimulus-evoked [Ca2+] responses to the underlying Ca2+ transport and buffering systems. Depolarization-evoked [Ca2+]i responses were studied in sympathetic neurons under voltage clamp, asking how response kinetics are defined by the Ca2+ handling systems expressed in these cells. We investigated five cases of increasing complexity, comparing observed and calculated responses deduced from measured Ca2+ handling properties. In Case 1, [Ca2+]i responses were elicited by small Ca2+ currents while Ca2+ transport by internal stores was inhibited, leaving plasma membrane Ca2+ extrusion intact. In Case 2, responses to the same stimuli were measured while mitochondrial Ca2+ uptake was active. In Case 3, responses were elicited as in Case 2 but with larger Ca2+ currents that produce larger and faster [Ca2+]i elevations. Case 4 included the mitochondrial Na/Ca exchanger. Finally, Case 5 included ER Ca2+ uptake and release pathways. We found that [Ca2+]i responses elicited by weak stimuli (Cases 1 and 2) could be quantitatively reconstructed using a spatially uniform model incorporating the measured properties of Ca2+ entry, removal, and buffering. Responses to strong depolarization (Case 3) could not be described by this model, but were consistent with a diffusion model incorporating the same Ca2+ transport and buffering descriptions, as long as endogenous buffers have low mobility, leading to steep radial [Ca2+]i gradients and spatially nonuniform Ca2+ loading by mitochondria. When extended to include mitochondrial Ca2+ release (Case 4) and ER Ca2+ transport (Case 5), the diffusion model could also account for previous measurements of stimulus-evoked changes in total mitochondrial and ER Ca concentration.

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SUMMARY1. The effects of perchlorate (Cl04-) on contraction have been studied in rat soleus muscle fibres using (i) potassium (K+) contracture and (ii) two-microelectrode-point voltage clamp techniques.2. Membrane potentials (l') at all external [K+] were 3-5 mV more negative in CO4-. The hyperpolarization could not be attributed to a change in Na', K+, or C1-permeability, or to an effect on the Na+-K' pump.3. C104-shifts the voltage dependence of tension activation, and contraction threshold, to more negative membrane potentials without altering maximrum tension. Consequently, twitches and submaximal K+ contractures were potentiated, whereas tetanic contractions and 200 mM-K+ contractures were unaltered.4. The decay of K+ contractures during steady depolarization with C104 developed a slow exponential phase with an average time constant of 6 05 + 0 76 min at -38 mV, and 1P68 + 0415 min at -19 mV. This slow component was (a) under the rapid control of the surface t' and (b) did not depend on external Ca2+.5. Inactivation of E-C coupling was measured with a test 200 mm-K+ depolarization following 3-10 min depolarizations in conditioning solutions containing 20-120 mM-K+. C104-induced a negative shift in the curve-relating test K+ contracture amplitude to conditioning Vm but did not alter the rate of repriming of tension upon repolarization.6. The results suggest that C104-increases the amount of activator produced during depolarization and thus allows the slow inactivation step in excitationcontraction (E-C) coupling to be reflected in the decay of K+ contracture tension.7. A 'perchlorate contracture', which did not depend on the activation of E-C coupling, was observed. The contracture depended on external Ca2+, but not on voltage-dependent Ca2+ channels or Na+-Ca2+ exchange.