Recruitment of Complete Right Bundle Branch Block by Permanent Para-Hisian Pacing.

His-bundle pacing has recently emerged as a means to maintain a physiological ventricular activation and eliminate the risk of pacing-induced myopathy associated with traditional right ventricular pacing. With His-bundle pacing, the exact stimulated structure and resulting excitation wavefront may be highly dependent on the pacing output, dimensions of the stimulatory electrodes, and orientation of the cathode and anode relative to the approximated conduction tissue and surrounding myocardium, owing to the juxtaposition of tissues with very different conduction properties. We herein present an 89-year-old woman with an infra-Hisian conduction disease in whom lower output pacing resulted in pure His-bundle pacing, and higher output pacing resulted in para-Hisian pacing that recruited diseased portions of the conduction system, narrowing the QRS complex.

Root-to-shoot transport of sulfate in Arabidopsis. Evidence for the role of SULTR3;5 as a component of low-affinity sulfate transport system in the root vasculature.

Xylem transport of sulfate regulates distribution of sulfur in vascular plants. Here, we describe SULTR3;5 as an essential component of the sulfate transport system that facilitates the root-to-shoot transport of sulfate in the vasculature. In Arabidopsis (Arabidopsis thaliana), SULTR3;5 was colocalized with the SULTR2;1 low-affinity sulfate transporter in xylem parenchyma and pericycle cells in roots. In a yeast (Saccharomyces cerevisiae) expression system, sulfate uptake was hardly detectable with SULTR3;5 expression alone; however, cells coexpressing both SULTR3;5 and SULTR2;1 showed substantial uptake activity that was considerably higher than with SULTR2;1 expression alone. The V(max) value of sulfate uptake activity with SULTR3;5-SULTR2;1 coexpression was approximately 3 times higher than with SULTR2;1 alone. In Arabidopsis, the root-to-shoot transport of sulfate was restricted in the sultr3;5 mutants, under conditions of high SULTR2;1 expression in the roots after sulfur limitation. These results suggested that SULTR3;5 is constitutively expressed in the root vasculature, but its function to reinforce the capacity of the SULTR2;1 low-affinity transporter is only essential when SULTR2;1 mRNA is induced by sulfur limitation. Consequently, coexpression of SULTR3;5 and SULTR2;1 provides maximum capacity of sulfate transport activity, which facilitates retrieval of apoplastic sulfate to the xylem parenchyma cells in the vasculature of Arabidopsis roots and may contribute to the root-to-shoot transport of sulfate.

Vacuolar sulfate transporters are essential determinants controlling internal distribution of sulfate in Arabidopsis.

Uptake of external sulfate from the environment and use of internal vacuolar sulfate pools are two important aspects of the acquisition of sulfur for metabolism. In this study, we demonstrated that the vacuolar SULTR4-type sulfate transporter facilitates the efflux of sulfate from the vacuoles and plays critical roles in optimizing the internal distribution of sulfate in Arabidopsis thaliana. SULTR4;1-green fluorescent protein (GFP) and SULTR4;2-GFP fusion proteins were expressed under the control of their own promoters in transgenic Arabidopsis. The fusion proteins were accumulated specifically in the tonoplast membranes and were localized predominantly in the pericycle and xylem parenchyma cells of roots and hypocotyls. In roots, SULTR4;1 was constantly accumulated regardless of the changes of sulfur conditions, whereas SULTR4;2 became abundant by sulfur limitation. In shoots, both transporters were accumulated by sulfur limitation. Vacuoles isolated from callus of the sultr4;1 sultr4;2 double knockout showed excess accumulation of sulfate, which was substantially decreased by overexpression of SULTR4;1-GFP. In seedlings, the supplied [(35)S]sulfate was retained in the root tissue of the sultr4;1 sultr4;2 double knockout mutant. Comparison of the double and single knockouts suggested that SULTR4;1 plays a major role and SULTR4;2 has a supplementary function. Overexpression of SULTR4;1-GFP significantly decreased accumulation of [(35)S]sulfate in the root tissue, complementing the phenotype of the double mutant. These results suggested that SULTR4-type transporters, particularly SULTR4;1, actively mediate the efflux of sulfate from the vacuole lumen into the cytoplasm and influence the capacity for vacuolar storage of sulfate in the root tissue. The efflux function will promote rapid turnover of sulfate from the vacuoles particularly in the vasculature under conditions of low-sulfur supply, which will optimize the symplastic (cytoplasmic) flux of sulfate channeled toward the xylem vessels.

Genes encoding proteins of the cation diffusion facilitator family that confer manganese tolerance.

The yeast Saccharomyces cerevisiae expressing a cDNA library prepared from Stylosanthes hamata was screened for enhanced Mn(2+) tolerance. From this screen, we identified four related cDNAs that encode membrane-bound proteins of the cation diffusion facilitator (CDF) family. One of these cDNAs (ShMTP1) was investigated in detail and found to confer Mn(2+) tolerance to yeast by internal sequestration rather than by efflux of Mn(2+). Expression of ShMTP1 in a range of yeast mutants suggested that it functions as a proton:Mn(2+) antiporter on the membrane of an internal organelle. Similarly, when expressed in Arabidopsis, ShMTP1 conferred Mn(2+) tolerance through internal sequestration. The ShMTP1 protein fused to green fluorescent protein was localized to the tonoplast of Arabidopsis cells but appeared to localize to the endoplasmic reticulum of yeast. We suggest that the ShMTP1 proteins are members of the CDF family involved in conferring Mn(2+) tolerance and that at least one of these proteins (ShMTP1) confers tolerance by sequestering Mn(2+) into internal organelles.