The interaction operates at the neuromuscular junction as well as on extrajunctional sarcolemma. The Na,K-ATPase ␣2 isozyme is enriched at the postsynaptic neuromuscular junction and co-localizes with nAChRs. The nAChR and Na,K-ATPase ␣ subunits specifically coimmunoprecipitate with each other, phospholemman, and caveolin-3. In a purified membrane preparation from Torpedo californica enriched in nAChRs and the Na,K-ATPase, a ouabain-induced conformational change of the Na,K-ATPase enhances a conformational transition of the nAChR to a desensitized state. These results suggest a mechanism by which the nAChR in a desensitized state with high apparent affinity for agonist interacts with the Na,K-ATPase to stimulate active transport. The interaction utilizes a membranedelimited complex involving protein-protein interactions, either directly or through additional protein partners. This interaction is expected to enhance neuromuscular transmission and muscle excitation. The nicotinic acetylcholine receptor (nAChR)2 and the Na,K-ATPase are integral membrane proteins that play key roles in membrane excitation. We previously identified a regulatory mechanism, termed acetylcholine (ACh)-induced hyperpolarization, whereby the nAChR and the Na,K-ATPase functionally interact to modulate the membrane potential of rat skeletal muscle (1-4). In this interaction, the binding of nanomolar concentrations of ACh to the nAChR stimulates electrogenic transport by the Na,K-ATPase ␣2 isozyme, causing a membrane hyperpolarization of about Ϫ4 mV. This effect requires prolonged exposure to nanomolar concentrations of nicotinic agonist. This property distinguishes it from the more well characterized, rapid action of micromolar concentrations of ACh, which open the nAChR and produce membrane depolarization (5). This finding suggested that a non-conducting conformation of the nAChR, rather than the open state, is involved in signaling to the Na,K-ATPase. In addition, it was shown that the nAChR and Na,K-ATPase can reciprocally interact in a membrane preparation from the Torpedo electric organ (1), a muscle-derived tissue that is rich in muscle nAChRs and Na,K-ATPase. This finding suggested that the nAChR and Na,K-ATPase may interact as part of a membrane-associated regulatory complex.Importantly, this regulation of Na,K-ATPase activity by the nAChR operates under the physiological conditions of normal muscle use. Its ACh concentration dependence is in the range of the residual ACh concentrations that remain in the muscle interstitial spaces for some time following nerve excitation, and to the ACh concentrations that arise at the neuromuscular junction (NMJ) from non-quantal ACh release. The later have also been shown to activate the Na,K-ATPase and hyperpolarize the end plate membrane (6, 7). Notably, this hyperpolariza-* This work was supported, in whole or in part, by National Institutes of Health

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Our previous finding that the muscle nicotinic acetylcholine receptor (nAChR) and the Na,K-ATPase interact as a regulatory complex to modulate Na,K-ATPase activity suggested that chronic, circulating nicotine may alter this interaction, with long-term changes in the membrane potential. To test this hypothesis, we chronically exposed rats to nicotine delivered orally for 21–31 days. Chronic nicotine produced a steady membrane depolarization of ∼3 mV in the diaphragm muscle, which resulted from a net change in electrogenic transport by the Na,K-ATPase α2 and α1 isoforms. Electrogenic transport by the α2 isoform increased (+1.8 mV) while the activity of the α1 isoform decreased (−4.4 mV). Protein expression of Na,K-ATPase α1 or α2 isoforms and the nAChR did not change; however, the content of α2 subunit in the plasma membrane decreased by 25%, indicating that its stimulated electrogenic transport is due to an increase in specific activity. The physical association between the nAChR, the Na,K-ATPase α1 or α2 subunits, and the regulatory subunit of the Na,K-ATPase, phospholemman (PLM), measured by co-immuno precipitation, was stable and unchanged. Chronic nicotine treatment activated PKCα/β2 and PKCδ and was accompanied by parallel increases in PLM phosphorylation at Ser63 and Ser68. Collectively, these results demonstrate that nicotine at chronic doses, acting through the nAChR-Na,K-ATPase complex, is able to modulate Na,K-ATPase activity in an isoform-specific manner and that the regulatory range includes both stimulation and inhibition of enzyme activity. Cholinergic modulation of Na,K-ATPase activity is achieved, in part, through activation of PKC and phosphorylation of PLM.

Double-differential cross sections for light-ion (p, d, t, 3 He and α) production in oxygen induced by 96 MeV neutrons are reported. Energy spectra are measured at eight laboratory angles from 20• to 160• in steps of 20• . Procedures for data taking and data reduction are presented. Deduced energy-differential and production cross sections are reported. Experimental cross sections are compared to theoretical reaction model calculations and experimental data at lower neutron energies in the literature. The measured proton data agree reasonably well with the results of the model calculations, whereas the agreement for the other particles is less convincing. The measured production cross sections for protons, deuterons, tritons and alpha particles support the

A new quasi-monoenergetic neutron beam facility has been constructed at The Svedberg Laboratory (TSL) in Uppsala, Sweden. Key features include a neutron energy range of 11-175 MeV, high fluxes, user flux control, flexible neutron field size and shape, and spacious and easily accessible user area. The first results of the beam characterisation measurements are reported.