Quantitative assessment of in vitro jets based on three-dimensional color Doppler reconstruction.

Three-dimensional (3-D) color Doppler imaging of flow jets was performed to investigate the effects of flow rate and orifice size on jet volumes. Flow jets were generated using a flow model to simulate mitral regurgitation. This flow model consisted of a ventricular chamber, a valvular plate and an atrial chamber. Steady flow was driven through circular orifices having diameters of 2.5, 3.5, 4.5, and 6 mm, respectively, with flow rates of 5, 10, 15, 20, and 25 mL/s to form free jets in the atrial chamber. An ATL Ultramark 9 HDI system was used to perform 3-D color Doppler imaging of the flow jets. A transesophageal probe was rotated by a stepper motor to create 3-D color Doppler images of the jets. The color jet volumes for different hemodynamic conditions were measured and then compared with the theoretical predictions. Results showed that the jet volume estimated from the 3-D color Doppler was directly proportional to the flow rate and inversely proportional to the orifice size. The estimated jet volumes correlated well (r > 0.95) with theoretical predictions. This study supports the use of color jet volume as a parameter to quantify mitral regurgitation.

A novel meprin beta' mRNA in mouse embryonal and human colon carcinoma cells.

Meprins, metalloendopeptidases of the astacin family, are composed of alpha and/or beta subunits and are expressed at high levels in mammalian renal and intestinal brushborder membranes. Only one mRNA has been identified previously for each of the subunits in adult human and rodent tissues; a 3.6-kilobase message for the alpha subunit and a 2.5-kilobase message for the beta subunit. The present study reports that a larger beta subunit message (2.7 kilobases, referred to as beta'), and no alpha subunit message, is expressed in embryonal carcinoma cell lines, F9 and Nulli-SSC1, and in human colon adenocarcinoma cells, HT-28-18-C1. Furthermore, in Nulli-SSC1 cells, the beta isoform is induced by the morphogen retinoic acid. The beta' isoform differs from beta only in a portion of the 5'-coding (corresponding to the signal and prosequence domains of the protein) and noncoding region. Only one gene was found for the beta subunit in the mouse and human genome. The deduced amino acid sequence of beta' has no homology with beta in the first 35 NH2-terminal residues, but the two sequences are identical after that. In vitro translation experiments indicated that the size of the protein product of beta' cDNA was similar to that of the beta cDNA protein product, and, in the presence of microsomal membranes, both were glycosylated. These studies indicate that the messages for the meprin beta and beta' subunit result from differential promoter usage and alternate splicing. Expression of the two isoforms may be regulated differentially depending on cell type and/or differentiation state of the cell.

The role of meprin A in the pathogenesis of acute renal failure.

Meprin A is a zinc-dependent metallo-endopeptidase that is present in the brush border membrane of renal proximal tubular epithelial cells. Although this enzyme has been detected in the kidney of mammalian species and its biochemical structure and action have been characterized, the role of this endopeptidase in normal renal physiology and in disease states is unknown. Therefore, we assessed the susceptibility of inbred strains of mice with normal and low meprin A activity to ischemic and nephrotoxic acute renal failure. We report that two normal meprin A strains of mice, C57BL/6 and DBA/2, developed more severe renal functional and structural injury following either bilateral renal artery clamping or the injection of hypertonic glycerol, compared to two low meprin A strains, C3H/He and CBA. These findings suggest that meprin A plays a role in the pathophysiology of acute renal failure following a variety of insults to the kidney. We propose that redistribution of this metalloendopeptidase to the basolateral membrane domain during acute renal failure results in degradation of the extracellular matrix and damage to adjacent peritubular structures.

Analysis of the factors involved in the retinoic acid-induced differentiation of a retinoid-hypersensitive embryonal carcinoma cell mutant.

Retinoic acid (RA) has been known to play an important role in cellular growth and differentiation as well as in vertebrate development. Many in vitro cell cultures also respond to RA by differentiating. Perhaps the most widely studied of these cultures are embryonal carcinoma (EC) cells. We have used an RA-hypersensitive EC cell mutant, created by retroviral insertion, to analyze the activity of the identifiable components in the RA response pathway. We have analyzed the mRNA expression patterns of the retinoic acid receptors (RARs) alpha, beta, and gamma, the retinoid X receptors (RXRs) alpha, beta, and gamma, and the cellular retinoic acid binding proteins (CRABPs) I and II. Our results indicate that CRABP I, RAR beta, and RAR gamma mRNAs are expressed differentially between parent and RA-hypersensitive mutant cells. All three messages are present at higher basal levels and at earlier times after RA addition in the mutant relative to parental cells. All other elements examined are equivalently expressed. Therefore analyses of the expression patterns of CRABPs, RARs, and RXRs in these RA-hypersensitive cells point to the probable importance of CRABP I, RAR beta, and RAR gamma in the RA induction pathway and also indicate that CRABP II and RXR gamma are not likely to be critical elements in the early differentiative response of cells to RA.