The action of aldosterone to increase apical membrane permeability in responsive epithelia is thought to be due to activation of sodium channels. Aldosterone stimulates methylation of a 95-kDa protein in apical membrane of A6 cells, and we have previously shown that methylation of a 95-kDa protein in the immunopurified Na ؉ channel complex increases open probability of these channels in planar lipid bilayers. We report here that aldosterone stimulates carboxylmethylation of the ␤ subunit of xENaC in A6 cells. In vitro translated ␤ subunit, but not ␣ or ␥, serves as a substrate for carboxylmethylation. Carboxylmethylation of ENaC reconstituted in planar lipid bilayers leads to an increase in open probability only when ␤ subunit is present. When the channel complex is immunoprecipitated from A6 cells and analyzed by Western blot with antibodies to the three subunits of xENaC, all three subunits are recognized as constituents of the complex. The results suggest that Na ؉ channel activity in A6 cells is regulated, in part, by carboxylmethylation of the ␤ subunit of xENaC.Aldosterone-stimulated sodium channel activity has been shown to involve methylation of membrane proteins (1, 2). Moreover, the aldosterone-induced increase in the activity of xENaC is blockable by the methylation inhibitor, 3-deazaadenosine (3). Sariban-Sohraby has demonstrated that aldosterone stimulates the methylation of a 90 -95-kDa protein in the apical membrane of A6 cells (4). We have previously shown that methylation of the 95-kDa subunit of an immunopurified renal sodium channel complex reconstituted in lipid bilayers results in increased sodium channel activity (5). In both studies the identity of the methylated protein is unknown.

Abstract.In this paper, we consider the boundary stabilization of a sandwich beam which consists of two outer stiff layers and a compliant middle layer. Using Riesz basis approach, we show that there is a sequence of generalized eigenfunctions, which forms a Riesz basis in the state space. As a consequence, the spectrum-determined growth condition as well as the exponential stability of the closed-loop system are concluded. Finally, the well-posedness and regularity in the sense of Salamon-Weiss class as well as the exact controllability are also addressed.Mathematics Subject Classification. 93C20, 93D15, 35D10, 47B06.

No abstract

In this paper, we consider a rotating system of elasticity. It consists of a disk, a flexible beam and a tip mass. The beam is assumed to be non-homogeneous (space depending of physical parameters). Moreover, the flexible beam is clamped at one end to the center of the disk, whereas a tip mass is attached to its other end. The disk rotates freely around its axis with a time-dependent angular velocity and the motion of the beam-mass is confined to a plane perpendicular to the disk. The system is shown to be exponentially stable under the action of: i) a torque control applied on the disk; ii) a force control and moment control or only a force control. Furthermore, the Riesz basis property is proved for the system in the case of uniform angular velocity.