Single-channel measurements of an N-acetylneuraminic acid-inducible outer membrane channel in Escherichia coli

NanC is an Escherichia coli outer membrane protein involved in sialic acid (Neu5Ac, i.e., N-acetylneuraminic acid) uptake. Expression of the NanC gene is induced and controlled by Neu5Ac. The transport mechanism of Neu5Ac is not known. The structure of NanC was recently solved (PDB code: 2WJQ) and includes a unique arrangement of positively charged (basic) side chains consistent with a role in acidic sugar transport. However, initial functional measurements of NanC failed to find its role in the transport of sialic acids, perhaps because of the ionic conditions used in the experiments. We show here that the ionic conditions generally preferred for measuring the function of outer-membrane porins are not appropriate for NanC. Single channels of NanC at pH 7.0 have: (1) conductance 100 pS to 800 pS in 100 mM: KCl to 3 M: KCl), (2) anion over cation selectivity (V (reversal) = +16 mV in 250 mM: KCl || 1 M: KCl), and (3) two forms of voltage-dependent gating (channel closures above ±200 mV). Single-channel conductance decreases by 50% when HEPES concentration is increased from 100 ?M: to 100 mM: in 250 mM: KCl at pH 7.4, consistent with the two HEPES binding sites observed in the crystal structure. Studying alternative buffers, we find that phosphate interferes with the channel conductance. Single-channel conductance decreases by 19% when phosphate concentration is increased from 0 mM: to 5 mM: in 250 mM: KCl at pH 8.0. Surprisingly, TRIS in the baths reacts with Ag|AgCl electrodes, producing artifacts even when the electrodes are on the far side of agar-KCl bridges. A suitable baseline solution for NanC is 250 mM: KCl adjusted to pH 7.0 without buffer

The problems of offenders with mental disorders: A plurality of perspectives within a single mental health care organisation

Managers, doctors, nurses, occupational therapists, social workers, psychologists, unqualified staff and service users were interviewed for a qualitative study of risk management and rehabilitation in an inner city medium secure forensic mental health care unit. Different professional orientations to service user problems were identified. Doctors focused primarily on the diagnosis of mental disorder, which they managed mainly through pharmaceutical interventions. Psychologists were principally concerned with personal factors, for example service user insight into their biographical history. Occupational therapists concentrated mainly on daily living skills, and social workers on post-discharge living arrangements. Some front line nurses, held accountable for security lapses, adopted a criminogenic approach. Service users were more likely than professionals to understand their needs in terms of their wider life circumstances. These differences are explored qualitatively in relation to four models of crossdisciplinary relationships: monoprofessional self-organisation combined with restricted communication; hermeneutic reaching out to other perspectives; the establishment of interdisciplinary sub-systems; and transdisciplinary merger. Relationships between professions working in this unit, as portrayed in qualitative interviews, corresponded mainly to the first model of monoprofessional self-organisation. Reasons for restricted crossdisciplinary understanding, particularly the wide power/status differences between the medical and other professions, and between staff and patients, are discussed