Small-conductance, Ca(2+) -activated K+ channel 2 is the key functional component of SK channels in mouse urinary bladder

Small-conductance Ca(2+)-activated K(+) (SK) channels play an important role in regulating the frequency and in shaping urinary bladder smooth muscle (UBSM) action potentials, thereby modulating contractility. Here we investigated a role for the SK2 member of the SK family (SK1-3) utilizing: 1) mice expressing beta-galactosidase (beta-gal) under the direction of the SK2 promoter (SK2 beta-gal mice) to localize SK2 expression and 2) mice lacking SK2 gene expression (SK2(-/-) mice) to assess SK2 function. In SK2 beta-gal mice, UBSM staining was observed, but staining was undetected in the urothelium. Consistent with this, urothelial SK2 mRNA was determined to be 4% of that in UBSM. Spontaneous phasic contractions in wild-type (SK2(+/+)) UBSM strips were potentiated (259% of control) by the selective SK channel blocker apamin (EC(50) = 0.16 nM), whereas phasic contractions of SK2(-/-) strips were unaffected. Nerve-mediated contractions of SK2(+/+) UBSM strips were also increased by apamin, an effect absent in SK2(-/-) strips. Apamin increased the sensitivity of SK2(+/+) UBSM strips to electrical field stimulation, since pretreatment with apamin decreased the frequency required to reach a 50% maximal contraction (vehicle, 21 +/- 4 Hz, n = 6; apamin, 12 +/- 2 Hz, n = 7; P < 0.05). In contrast, the sensitivity of SK2(-/-) UBSM strips was unaffected by apamin. Here we provide novel insight into the molecular basis of SK channels in the urinary bladder, demonstrating that the SK2 gene is expressed in the bladder and that it is essential for the ability of SK channels to regulate UBSM contractility.

Soluble expression and characterization of a GFP-fused pea actin isoform (PEAc1)

A pea actin isoform PEAc1 with green fluorescent protein (GFP) fusion to its C-terminus and His-tag to its N-terminus, was expressed in prokaryotic cells in soluble form, and highly purified with Ni-Chelating Sepharose Fast Flow column. The purified fusion protein (PEAc1-GFP) efficiently inhibited DNase I activities before polymerization, and activated the myosin Mg-ATPase activities after polymerization. The PEAc1-GFP also polymerized into green fluorescent filamentous structures with a critical concentration of 0.75 uM. These filamentous structures were labeled by TRITC-phalloidin, a specific agent for staining actin microfilaments, and identified as having 9 nm diameters by negative staining. These results indicated that PEAc1 preserved the essential characteristics of actin even with His-tag and GFP fusion, suggesting a promising potential to use GFP fusion protein in obtaining soluble plant actin isoform to analyze its physical and biochemical properties in vitro. The PEAc1-GFP was also expressed in tobacco BY2 cells, which offers a new pathway for further studying its distribution and function in vivo.

[Determination of deoxyribonucleic acid with neutral red by resonance light scattering method]

The method is based on the enhancement effect of the resonance light scattering (RLS) due to the long range assembly of neutral red (NR) on the molecular surface of DNA. The RLS of NR is greatly enhanced by DNA in the pH range of 5.0-7.0. The enhanced intensity of RLS at 335.0 nm is proportional to the concentration of DNA in the range 0-600 ng.mL-1. The detection limit is 12.8 ng.mL-1. This method is simple, rapid and has been applied to the determination of DNA in mixed samples with satisfactory results.

RhoB is dispensable for mouse development, but it modifies susceptibility to tumor formation as well as cell adhesion and growth factor signaling in transformed cells

RhoB is an endosomal small GTPase that is implicated in the response to growth factors, genotoxic stress, and farnesyltransferase inhibitors. To gain insight into its physiological functions we examined the consequences of homozygous gene deletion in the mouse. Loss of RhoB did not adversely affect mouse development, fertility, or wound healing. However, embryo fibroblasts cultured in vitro exhibited a defect in motility, suggesting that RhoB has a role in this process that is conditional on cell stress. Neoplastic transformation by adenovirus E1A and mutant Ras yielded differences in cell attachment and spreading that were not apparent in primary cells. In addition, transformed -/- cells displayed altered actin and proliferative responses to transforming growth factor beta. A negative modifier role in transformation was suggested by the increased susceptibility of -/- mice to 7,12-dimethylbenz[a]anthracene-induced skin carcinogenesis and by the increased efficiency of intraperitoneal tumor formation by -/- cells. Our findings suggest that RhoB is a negative regulator of integrin and growth factor signals that are involved in neoplastic transformation and possibly other stress or disease states.

[Determination of deoxyribonucleic acid with rosaniline by a resonance light scattering method]

The resonance light scattering (RLS) spectra of Rosaniline with DNA have been studied. The RLS of Rosaniline is greatly enhanced by DNA in pH range of 10.5-10.8. There is a resonance light scattering peak ofat 485 nm, and the enhanced intensity of RLS at this wavelength is proportional to the concentration of DNA. The linear range of the calibration graph is 0-1.00 mg.L-1 with the correlation coefficient of 0.9980. The detection limit is 14.2 ng.mL-1. The relative standard deviation(n = 10) was within 2.1%. This method is simple, rapid and has been applied to the determination of DNA in mixed samples with satisfactory results.

AKT2, a member of the protein kinase B family, is activated by growth factors, v-Ha-ras, and v-src through phosphatidylinositol 3-kinase in human ovarian epithelial cancer cells

Three members have been identified in the protein kinase B (PKB) family, i.e., Akt/PKB alpha, AKT2/PKB beta, and AKT3/PKB gamma. Previous studies have demonstrated that only AKT2 is predominantly involved in human malignancies and has oncogenic activity. However, the mechanism of transforming activity of AKT2 is still not well understood. Here, we demonstrate the activation of AKT2 with several growth factors, including epidermal growth factor, insulin-like growth factor 1, insulin-like growth factor II, basic fibroblast growth factor, platelet-derived growth factor, and insulin, in human ovarian epithelial cancer cells. The kinase activity and the phosphorylation of AKT2 were induced by the growth factors and blocked by the phosphatidylinositol (PI) 3-kinase inhibitor, wortmannin, and dominant-negative Ras (N17Ras). Moreover, the activated Ras and v-Src, two proteins that transduce growth factor-generated signals, also activated AKT2, and this activation was not significantly enhanced by growth factor stimulation but was abrogated by wortmannin. These results indicate that AKT2 is a downstream target of PI 3-kinase and that Ras and Src function upstream of PI 3-kinase and mediate the activation of AKT2 by growth factors. The findings also provide further evidence that AKT2, in cooperation with Ras and Src, is important in the development of some human malignancies.

Potassium currents in Drosophila: different components affected by mutations of two genes

Electrophysiological analysis of the Drosophila behavioral mutants Eag and Sh and the double mutant Eag Sh indicates that the products of both genes take part in the control of potassium currents in the membranes of both nerve and muscle. In voltage-clamped larval muscle fibers, Sh affects the transient A current, whereas Eag reduces the delayed rectification and, to a lesser extent, the A current.