The development of the thymus depends initially on epithelial-mesenchymal and subsequently on reciprocal lympho-stromal interactions. The genetic steps governing development and differentiation of the thymic microenvironment are unknown. With the use of a targeted disruption of the whn gene, which recapitulates the phenotype of the athymic nude mouse, the WHN transcription factor was shown to be the product of the nude locus. Formation of the thymic epithelial primordium before the entry of lymphocyte progenitors did not require the activity of WHN. However, subsequent differentiation of primitive precursor cells into subcapsular, cortical, and medullary epithelial cells of the postnatal thymus did depend on activity of the whn gene. These results define the first genetically separable steps during thymic epithelial differentiation.

We cloned two L L subunits of large-conductance calcium-activated potassium (BK) channels, hKCNMB3 (BKL L1) and hKCNMB4 (BKL L4). Profiling mRNA expression showed that hKCNMB3 expression is enriched in testis and hKCNMB4 expression is very prominent in brain. We coexpressed BK channel K K (BKK K) and BKL L4 subunits in vitro in CHO cells. We compared BKK K/L L4 mediated currents with those of smooth muscle BKK K/L L1 channels. BKL L4 slowed activation kinetics more significantly, led to a steeper apparent calcium sensitivity, and shifted the voltage range of BK current activation to more negative potentials than BKL L1. BKK K/L L4 channels were not blocked by 100 nM charybdotoxin or iberiotoxin, and were activated by 17L L-estradiol.z 2000 Federation of European Biochemical Societies.

Large-conductance potassium (BK) channels in vascular smooth muscle cells (VSMCs) sense both changes in membrane potential and in intracellular Ca(2+) concentration. BK channels may serve as negative feedback regulators of vascular tone by linking membrane depolarization and local increases in intracellular Ca(2+) concentration (Ca(2+) sparks) to repolarizing spontaneous transient outward K(+) currents (STOCs). BK channels are composed of channel-forming BKalpha and auxiliary BKbeta1 subunits, which confer to BK channels an increased sensitivity for changes in membrane potential and Ca(2+). To assess the in vivo functions of this ss subunit, mice with a disrupted BKbeta1 gene were generated. Cerebral artery VSMCs from BKbeta1 -/- mice generated Ca(2+) sparks of normal amplitude and frequency, but STOC frequencies were largely reduced at physiological membrane potentials. Our results indicate that BKbeta1 -/- mice have an abnormal Ca(2+) spark/STOC coupling that is shifted to more depolarized potentials. Thoracic aortic rings from BKbeta1 -/- mice responded to agonist and elevated KCl with a increased contractility. BKbeta1 -/- mice had higher systemic blood pressure than BKbeta1 +/+ mice but responded normally to alpha(1)-adrenergic vasoconstriction and nitric oxide-mediated vasodilation. We propose that the elevated blood pressure in BKbeta1 -/- mice serves to normalize Ca(2+) spark/STOC coupling for regulating myogenic tone. The full text of this article is available at http://www.circresaha.org.