Sarcomere length and first-order diffraction line width were measured by laser diffraction during elongation of activated frog tibialis anterior muscle fiber bundles (i.e., eccentric contraction) at nominal fiber strains of 10, 25, or 35% (n = 18) for 10 successive contractions. Tetanic tension, measured just before each eccentric contraction, differed significantly among strain groups and changed dramatically during the 10-contraction treatment (P < 0.01). Average maximum tetanic tension for the three groups measured before any treatment was 203.7 +/- 6.8 kN/m2, but after the 10-eccentric contraction sequence decreased to 180.3 +/- 3.8, 125.1 +/- 7.8, and 78.3 +/- 5.1 kN/m2 for the 10, 25, and 35% strain groups, respectively (P < 0.0001). Addition of 10 mM caffeine to the bathing medium decreased the loss of tetanic tension in the 10% strain group but had only a minimal effect on either the 25 or 35% strain groups. Diffraction pattern line width, a measure of sarcomere length heterogeneity, increased significantly with muscle activation and then continued to increase with successive stretches of the activated muscle. Line width increase after each stretch was significantly correlated with the lower yield tension of the successive contractile record. These data demonstrate a direct association and, perhaps, a causal relationship between sarcomere strain and fiber bundle injury. They also demonstrate that muscle injury is accompanied by a progressive increase in sarcomere length heterogeneity, yielding lower yield tension as injury progresses.

Interfacial water lying next to hydrophilic surfaces has been shown to be spectroscopically, mechanically, and electrically distinct from bulk water. Interfacial water has also been shown to exclude negatively- and positively-charged microspheres, and has thus become known as the “exclusion zone.” Measurements have demonstrated that exclusion zones exhibit a negative electrical potential on the order of −100 mV relative to bulk water, with a corresponding distribution of positive protons in the bulk water region beyond the exclusion zone. This separation of charge is hypothesized to create an electrostatic force between the exclusion zone and the proton-enriched zone beyond. To test this hypothesis, a hydrophilic Nafion ring was attached to the tip of a deflectable ribbon-like force sensor. The sensor was designed to obstruct the flow of protons from one side of the lever to the other, so that any proton-based force would remain unilateral. pH-sensitive dye measurements confirmed that the protons were largely confined to one side. When the lever assembly was exposed to water, the sensor deflected toward the protons. Over a period of 20 min, deflection amounted to approximately 20 μm, corresponding to a force of approximately 22 μN. Hence, electrostatic forces are confirmed. If exclusion zones exist ubiquitously at hydrophilic surfaces, including biological surfaces, then the resulting electrostatic forces may play significant roles in many biological phenomena including adhesion and protein folding.

Protein–water interaction plays a crucial role in protein dynamics and hence function. To study the chemical environment of water and proteins with high spatial resolution, synchrotron radiation-Fourier transform infrared (SR-FTIR) spectromicroscopy was used to probe skeletal muscle myofibrils. Observing the OH stretch band showed that water inside of relaxed myofibrils is extensively hydrogen-bonded with little or no free OH. In higher-resolution measurements obtained with single isolated myofibrils, the water absorption peaks were relatively higher within the center region of the sarcomere compared to those in the I-band region, implying higher hydration capacity of thick filaments compared to the thin filaments. When specimens were activated, changes in the OH stretch band showed significant dehydrogen bonding of muscle water; this was indicated by increased absorption at ∼3480 cm–1 compared to relaxed myofibrils. These contraction-induced changes in water were accompanied by splitting of the amide I (C=O) peak, implying that muscle proteins transition from α-helix to β-sheet-rich structures. Hence, muscle contraction can be characterized by a loss of order in the muscle–protein complex, accompanied by a destructuring of hydration water. The findings shed fresh light on the molecular mechanism of muscle contraction and motor protein dynamics.

A minimally-invasive diagnosis of pancreatic cancer is accomplished by obtaining a fine needle aspirate and observing the cell preparations under conventional optical microscopy. As an unavoidable artifact, native tissue architecture is lost, making definite diagnosis of malignancy, or invasive neoplasm, impossible. One solution is the preparation of core biopsies (CBs) within a microfluidic device that are subsequently imaged in 3D. In this paper, porcine pancreas CBs (L = 1-2 cm, D = 0.4-2.0 mm) were formalin-fixed, stained and optically cleared (FocusClear ® ). In brightfield at 40x, light transmission through the ordinarily opaque CBs was increased 5-15x, and internal islet structures were easily identified 250-300 μm beneath the tissue surface. Typically, specimen preparation is time intensive and requires precise handling since CBs are delicate; thus, fixative, absorptive stain and FocusClear ® diffusion were done slowly and manually. To significantly speed up tissue processing, we developed a microfluidic device consisting of both a main channel (L = 12.5 cm, D = 1.415 mm) with a circular cross section used for fixing and transporting the CB and an intersecting U-channel employed for staining. Space between the CB and channel wall provided a key feature not traditionally employed in microfluidic devices, such that at low flow rates (5-10 mL/min) CBs were fixed and stained while the specimen remained stationary. By switching quickly to higher flow rates (15-20 mL/min), we could precisely overcome adhesion and transport the specimen within the channel towards the imaging platform for 3D pathology.

No abstract