High potassium diets lead to an inverse regulation of sodium and magnesium absorption in ruminants, suggesting some form of cross talk. Previous Ussing chamber experiments have demonstrated a divalent sensitive Na(+) conductance in the apical membrane of ruminal epithelium. Using patch-clamped ruminal epithelial cells, we could observe a divalent sensitive, nonselective cation conductance (NSCC) with K(+) permeability > Cs(+) permeability > Na(+) permeability. Conductance increased and rectification decreased when either Mg(2+) or both Ca(2+) and Mg(2+) were removed from the internal or external solution or both. The conductance could be blocked by Ba(2+), but not by tetraethylammonium (TEA). Subsequently, we studied this conductance measured as short-circuit current (I(sc)) in Ussing chambers. Forskolin, IBMX, and theophylline are known to block both I(sc) and Na transport across ruminal epithelium in the presence of divalent cations. When the NSCC was stimulated by removing mucosal calcium, an initial decrease in I(sc) was followed by a subsequent increase. The cAMP-mediated increase in I(sc) was reduced by low serosal Na(+) and serosal addition of imipramine or serosal amiloride and depended on the availability of mucosal magnesium. Luminal amiloride had no effect. Flux studies showed that low serosal Na(+) reduced (28)Mg fluxes from mucosal to serosal. The data suggest that cAMP stimulates basolateral Na(+)/Mg(2+) exchange, reducing cytosolic Mg. This increases sodium uptake through a magnesium-sensitive NSCC in the apical membrane. Likewise, the reduction in magnesium uptake that follows ingestion of high potassium fodder may facilitate sodium absorption, as observed in studies of ruminal osmoregulation. Possibly, grass tetany (hypomagnesemia) is a side effect of this useful mechanism.

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New-generation 0.55T systems require a suite of tailored coils to preserve image quality that is expected from higher field systems. We built a six-channel coil array for knee MRI using RG58 coaxial cable loops, which have adequate mechanical flexibility to wrap tightly around the leg and suitably low conductive loss at 23.55MHz. Initial findings show that the dedicated coil outperformed a general-purpose counterpart and suggest that clinical quality knee imaging is feasible.

Diffusion-weighted imaging in renal tissue is a complex interplay of microstructural and microcirculation effects, which are often quantified with diffusion tensor imaging (DTI) or intravoxel incoherent motion (IVIM), as well as hybrid models such as Renal Flow and Microstructure AnisotroPy (REFMAP). This work measures the modulation of these effects with cardiac phase and with flow compensated (FC) diffusion gradient waveforms. Results show that both cardiac phase and FC affect diffusion metrics signficantly in cortex and medulla, and suggest that these experimental tools may in the future be leveraged to increase biophysical specificity of renal diffusion MRI metrics.

New generation low-field MRI systems can be ideal for MRI-guided interventions due to wide bore diameters and lower susceptibility artifacts improving patient access and needle visualization, respectively. We evaluated a set of pulse sequences for their suitability for needle visualization using a new-generation 0.55T system and compared the results with those of a clinical 3T system. Interventional needles can be adequately visualized at 0.55T. Using TSE pulse sequences, needle artifacts display more favorable at 0.55T than 3T. SEMAC and HASTE pulse sequences may not facilitate diagnostic needle visualization at 0.55T but are not needed for clinical MR interventions.