Subtle changes in crosslinking drive diverse anomalous transport characteristics in actin-microtubule networks.

Anomalous diffusion in crowded and complex environments is widely studied due to its importance in intracellular transport, fluid rheology and materials engineering. Specifically, diffusion through the cytoskeleton, a network comprised of semiflexible actin filaments and rigid microtubules that interact both sterically and via crosslinking, plays a principal role in viral infection, vesicle transport and targeted drug delivery. Here, we elucidate the impact of crosslinking on particle diffusion in composites of actin and microtubules with actin-actin, microtubule-microtubule and actin-microtubule crosslinking. We analyze a suite of transport metrics by coupling single-particle tracking and differential dynamic microscopy. Using these complementary techniques, we find that particles display non-Gaussian and non-ergodic subdiffusion that is markedly enhanced by cytoskeletal crosslinking, which we attribute to suppressed microtubule mobility. However, the extent to which transport deviates from normal Brownian diffusion depends strongly on the crosslinking motif - with actin-microtubule crosslinking inducing the most pronounced anomalous characteristics. Our results reveal that subtle changes to actin-microtubule interactions can have complex impacts on particle diffusion in cytoskeleton composites, and suggest that a combination of reduced filament mobility and more variance in actin mobilities leads to more strongly anomalous particle transport.

Paraplegia resulting from vessel ligation.

STUDY DESIGN: This is a retrospective review of clinical records for evidence of paraplegia specifically resulting from segmental vessel ligation during anterior spinal surgery. OBJECTIVES: To determine the precise risk rate, and to potentially identify risk factors. SUMMARY OF BACKGROUND DATA: Although many authors have alluded to this risk, the exact risk rate and risk factors have never been identified. METHODS: All patients having an anterior approach involving T1-L3 were reviewed. The two reviewers were not involved in any of the surgeries. The 1197 cases were consecutive from 1967 to 1991. RESULTS: There were no paralyses. CONCLUSIONS: There would appear to be virtually no risk to segmental vessel ligation provided: 1) vessel ligation is unilateral, 2) done on the convexity of a scoliosis, 3) ligated at midvertebral body level, and 4) hypotensive anesthesia is avoided. Soft clamping with somatosensory-evoked potential monitoring does not appear justified.

Retrograde aortic dissection occurring during cardiopulmonary bypass. Successful repair and concominant subclavian-to-coronary artery vein bypass.

A retrograde aortic dissection that occurred during cardiopulmonary bypass was successfully repaired. The cause of dissection was related to the jet of retrograde perfusion. The use of subclavian-to-coronary artery vein bypass when the ascending aorta is not suitable for vein anastomosis because of dissection or aneurysms appears to be a satisfactory alternative to aorta-coronary bypass.