The interaction of Na(+) and K(+) in the pore of cyclic nucleotide-gated channels

The permeability ratio between K(+) and Na(+) ions in cyclic nucleotide-gated channels is close to 1, and the single channel conductance has almost the same value in the presence of K(+) or Na(+). Therefore, K(+) and Na(+) ions are thought to permeate with identical properties. In the alpha-subunit from bovine rods there is a loop of three prolines at positions 365 to 367. When proline 365 is mutated to a threonine, a cysteine, or an alanine, mutant channels exhibit a complex interaction between K(+) and Na(+) ions. Indeed K(+), Rb(+) and Cs(+) ions do not carry any significant macroscopic current through mutant channels P365T, P365C and P365A and block the current carried by Na(+) ions. Moreover in mutant P365T the presence of K(+) in the intracellular (or extracellular) medium caused the appearance of a large transient inward (or outward) current carried by Na(+) when the voltage command was quickly stepped to large negative (or positive) membrane voltages. This transient current is caused by a transient potentiation, i.e., an increase of the open probability. The permeation of organic cations through these mutant channels is almost identical to that through the wild type (w.t.) channel. Also in the w.t. channel a similar but smaller transient current is observed, associated to a slowing down of the channel gating evident when intracellular Na(+) is replaced with K(+). As a consequence, a rather simple mechanism can explain the complex behavior here described: when a K(+) ion is occupying the pore there is a profound blockage of the channel and a potentiation of gating immediately after the K(+) ion is driven out. Potentiation occurs because K(+) ions slow down the rate constant K(off) controlling channel closure. These results indicate that K(+) and Na(+) ions do not permeate through CNG channels in the same way and that K(+) ions influence the channel gating.     

Flow cytometry of uveal melanomas

Tumor cell kinetic parameters were determined for 36 uveal melanomas retained in fixed tissue sections using flow cytometric techniques and computerized morphometry. By flow cytometry the majority of cells comprising the 36 tumors were in the G0/G1 phase (55.7%). The DNA index was 1.40 +/- 0.57 units. Using Spearman's rank order correlation test, the correlation between DNA index and the inverse standard deviation of nucleolar area was found to be statistically significant. The potential usefulness of flow cytometry in predicting tumors of high malignant potential is discussed.     

Cyclic nucleotide-gated channels. Pore topology studied through the accessibility of reporter cysteines.

In voltage- and cyclic nucleotide-gated ion channels, the amino-acid loop that connects the S5 and S6 transmembrane domains, is a major component of the channel pore. It determines ion selectivity and participates in gating. In the alpha subunit of cyclic nucleotide-gated channels from bovine rod, the pore loop is formed by the residues R345-S371, here called R1-S27. These 24 residues were mutated one by one into a cysteine. Mutant channels were expressed in Xenopus laevis oocytes and currents were recorded from excised membrane patches. The accessibility of the substituted cysteines from both sides of the plasma membrane was tested with the thiol-specific reagents 2-aminoethyl methanethiosulfonate (MTSEA) and [2-(trimethylammonium)ethyl]methanethiosulfonate (MTSET). Residues V4C, T20C, and P22C were accessible to MTSET only from the external side of the plasma membrane, and to MTSEA from both sides of the plasma membrane. The effect of MTSEA applied to the inner side of T20C and P22C was prevented by adding 10 mM cysteine to the external side of the plasma membrane. W9C was accessible to MTSET from the internal side only. L7C residue was accessible to internal MTSET, but the inhibition was partial, approximately 50% when the MTS compound was applied in the absence of cGMP and 25% when it was applied in the presence of cGMP, suggesting that this residue is not located inside the pore lumen and that it changes its position during gating. Currents from T15C and T16C mutants were rapidly potentiated by intracellular MTSET. In T16C, a slower partial inhibition took place after the initial potentiation. Current from I17C progressively decayed in inside-out patches. The rundown was accelerated by inwardly applied MTSET. The accessibility results of MTSET indicate a well-defined topology of the channel pore in which residues between L7 and I17 are inwardly accessible, residue G18 and E19 form the narrowest section of the pore, and T20, P21, P22 and V4 are outwardly accessible.     

Characterization and properties of a novel plasmid vector for Bacillus thuringiensis displaying compatibility with host plasmids.

A novel plasmid vector, composed of a 1.7-kb Bacillus thuringiensis (B.t.) replicon, a multiple cloning site, and an erythromycin-resistance marker gene from Bacillus subtilis, was constructed for use in B.t. Unlike other vectors which have been reported to be acceptable for B.t., this new B.t. vector was stably maintained in the absence of Er and did not displace host plasmids, some of which carry crystal protein-encoding genes (cry genes). The compatibility of this B.t. vector with native plasmids is highly desirable when introducing new cry genes into a wild-type B.t. strain. When a cryIIIA gene of B.t. tenebrionis was cloned in this vector and introduced into B.t. kurstaki (kur) HD119, cryIIIA was highly expressed without affecting the level of expression of native cry genes. The stability of this vector and its compatibility with native B.t. plasmids were achieved by subcloning only nucleotide sequences required for the vector to replicate in B.t. The origin of replication was first cloned on a 9.6-kb Bg/II fragment from a 75-kb plasmid of B.t. kur HD73 and then localized to a 2.4-kb region within the 9.6-kb fragment. Sequencing of the 2.4-kb region revealed the presence of an open reading frame (ORF), encoding a putative 312-amino acid (aa) protein. The deduced aa sequence of the ORF showed no homology to any published aa sequences. Deletion analysis indicated that the B.t. vector required at least the ORF and up to 300 bp surrounding the ORF, in order to replicate.     

Reproducibility of nucleolar measurements in human intraocular melanoma cells on standard histologic microslides

The standard deviation of nucleolar area (SDNA), as determined by semiautomated measurement of routinely prepared histologic sections, has been shown to be an effective predictor of mortality for human intraocular melanoma. One hundred cases of this tumor underwent two independent determinations of SDNA by each of two technicians using the same device. One technician performed the two measurements within two months, the other within three weeks. Analysis of these 400 values revealed the following: the more experienced of the two technicians achieved an acceptable level of reproducibility in determining SDNA; the less-experienced technician achieved a lower level of reproducibility; a systematic bias was found upon comparing SDNA values of the two technicians; and this bias can be partially corrected by applying a linear transform. These findings support the value of SDNA as a practical clinical measure of malignant potential for intraocular melanoma but also suggest that experience can enhance the reproducibility of a technician's measurements.     

The scoliosis (sco) mouse: a new allele of Pax1

We describe the spontaneous mutant mouse scoliosis (sco) that carries a new allele of Pax1 (un-i, undulated intermediate). The Pax1(un-i) allele is lacking the 5'-flanking region and exon 1 to 4 which is mapped to nt -2636 to -640 and -272 to 4271 of the Pax1 gene. Homozygous mice show a mild form of the known phenotypes of other Pax1 mutants. Adult mice have a lumbar scoliosis and kinky tails. In homozygous embryos the skeleton ossifies early, ossification centers of the vertebral bodies are fused with the ossification centers of the pedicles. Neural arches and spinous processes are underdeveloped but the pedicles and transverse processes are overdeveloped which is in contrast to other Pax1 mutants. In the scapula, the acromion is missing and the deltoid tuberosity of the proximal humerus is shortened and thickened. Among the inner organs the thymus development is affected. In late embryos, the thymus is small and thymocyte numbers are reduced. T-cell development from CD4- and CD8- double negative (DN) to CD4+ and CD8+ double positive (DP) is decelerated. The percentage of CD90+ cells is also reduced but in contrast to other Pax1 mutants no alteration of the expression level of the CD90 (Thy-1) could be found.     

Inheritance and regression toward the mean in heterogeneous cell populations

Traits such as birth size and lifetime can vary widely even among non-mutated progeny of the same cell proliferating in the same environment. On the other hand, population parameters of these traits may remain stable over many generations, and there may be a distinct inheritance of these traits from mother to daughters. We have reconsidered the implication of mother-daughter correlations in light of linear regression analysis. It is proposed that a non-mutant cell whose phenotype deviates from the population mean produces progeny whose rate of regression toward the mean is proportional to 1-r, where r is the mother-daughter correlation coefficient of the trait under study. Theoretical support for this proposition is derived from linear regression analysis. Empirical support is found in pedigree analysis of cell growth constants among NIH3T3 mouse fibroblast cells, where the presence of an activated human ras oncogene is associated with a decreased r and an increased rate at which the growth constants of progeny regress toward the population mean.     

Statistical methods for the practical clinical application of morphometric measurements

Four statistical methods are presented to determine the practical clinical value of measurements made from malignant tumors and to translate these measurements into a prediction of survival for each patient: the Cox statistical model, which must be derived from a data base of cases with known outcome; the null-rank test, a modified rank-sum test that provides an overall measure of the effectiveness of the Cox model; the predicted survival curve, an estimate of survival derived for each new patient from measurements of the primary tumor; and the standard error of measurement, an empirical method for estimating the variability introduced into predicted survival by errors in measurement. The value of these statistical methods was demonstrated by application to 200 cases of human intraocular melanoma, with the two predictive morphometric measurements used being the standard deviation of nucleolar area (SDNA) and the largest tumor dimension (LTD) derived from a single histologic slide of each tumor. Sufficient references and mathematical details are provided to allow anyone with moderate skills as a computer programmer to construct or obtain all of the relevant algorithms.     

Histological and ultrastructural features of gastrointestinal basidiobolomycosis

Basidiobolus ranarum is a fungus found in the dung of amphibians, reptiles, and insectivorous bats. Its structural elements include both hyphae and zygospores. Patients with B. ranarum infection may present with subcutaneous, gastrointestinal, or systemic lesions. Here we report a case of gastrointesinal badidiomycosis in a 13-year-old male child who presented with acute abdomen. Exploration revealed a mass in the ascending colon. On histology, transmural granulomatous inflammation composed of abundant eosinophils, lymphocytes, histiocytes and giant cells was seen. Histochemical stains revealed broad, non-septate, hyphae-like structures surrounded by an eosinophilic sheath. On an ultrastructural level, fungal hyphae, spores, and macrophage-laden crystalloids were observed. The diagnosis of gastrointestinal basidiobolomycosis was established and the patient received antifungal treatment. This paper reviews the relevant literature regarding basidiomycosis, and discusses its diverse clinicopathological features, as well as distinguishing it from other diseases.