Actomyosin kinetics in both skinned skeletal muscle fibers at maximum Ca2+-activation and unregulated in vitro motility assays are modulated by solvent microviscosity in a manner consistent with a diffusion limited process. Viscosity might also influence cardiac thin filament Ca2+-regulatory protein dynamics. In vitro motility assays were conducted using thin filaments reconstituted with recombinant human cardiac troponin and tropomyosin; solvent microviscosity was varied by addition of sucrose or glucose. At saturating Ca2+, filament sliding speed (s) was inversely proportional to viscosity. Ca2+-sensitivity (pCa50) of s decreased markedly with elevated viscosity (η/η0 ≥ ~1.3). For comparison with unloaded motility assays, steady-state isometric force (F) and kinetics of isometric tension redevelopment (kTR) were measured in single, permeabilized porcine cardiomyocytes when viscosity surrounding the myofilaments was altered. Maximum Ca2+-activated F changed little for sucrose ≤ 0.3 M (η/η0 ~1.4) or glucose ≤ 0.875 M (η/η0 ~1.66), but decreased at higher concentrations. Sucrose (0.3 M) or glucose (0.875 M) decreased pCa50 for F. kTR at saturating Ca2+ decreased steeply and monotonically with increased viscosity but there was little effect on kTR at sub-maximum Ca2+. Modeling indicates that increased solutes affect dynamics of cardiac muscle Ca2+-regulatory proteins to a much greater extent than actomyosin cross-bridge cycling.

SummaryBackground:Bacteria in the Pantoea genus are plant and soil associated Gram-negative rods described as nosocomial pathogens and as rare causes of community-acquired infections. The latter have been classically associated with gardening and plant thorn injuries and immunocompromised states are additional risk factors. We report a patient with pica and geophagia, Pantoea sepsis, and sickle cell crisis, associations not previously described.Case Report:A 23-year-old pregnant female presented to the emergency department with sickle cell pain crisis. On the third day of hospitalization the patient developed fever subsequently determined to be caused by Pantoea bacteremia and sepsis. She was successfully treated with a two-week course of ceftriaxone. The patient admitted to a habit of frequently eating large amounts of soil and this geophagia had increased since she became pregnant. She had marked clinical improvement with treatment and she was counseled to stop eating soil.Conclusions:This is the first reported case of Pantoea infection possibly associated with geophagia and the first reported case of Pantoea bacteremia and sepsis related to an episode of sickle cell crisis.