Diffusion models of ion-channel gating and the origin of power-law distributions from single-channel recording.

The lifetimes of the unitary currents from ion channels, as revealed from single-channel recording, are traditionally thought to follow exponential or multiexponential distributions. The interpretation of these event-time distributions is that the gating process follows Markov kinetics among a small number of states. There is recent evidence, however, that certain systems exhibit distributions that follow power laws or functions related to power laws. Likewise, it has been suggested that data sets that appear to be multiexponential may be fit to simple power laws as well. In this paper we propose a different view of ion-channel-gating kinetics that is consistent with these recent experimental observations. We retain the Markovian nature of the kinetics, but, in contrast to the traditional models, we suggest that ion-channel proteins have a very large number of states all of similar energy. Gating, therefore, resembles a diffusion process. We show that our simplest one-dimensional model exhibits single-channel distributions that follow power laws of the form t-a, where 1/2 less than or equal to a less than or equal to 3/2. Exponents determined from recent experiments approximately fall within this range. We believe that this model is consistent with modern views of protein dynamics and, thus, may provide a key to the molecular details of the gating process.     

Apha-adrenergic receptor blockade increases human REM sleep.

1 An alpha-adrenergic receptor blocking agent, thymoxamine (150 mg i.v.) in the early night sleep of young adults increased REM sleep duration and also brief awakenings in the early night, while slow wave sleep, stage 3+4, was diminished. In the later night, however, stage 3+4 sleep was increased. Control experiments demonstrated that thymoxamine (i.v.) was without effect on blood pressure. 2 REM sleep duration may be inversely proportional to noradrenaline available at central alpha-adrenoceptors, but the control mechanisms for REM sleep appear interdependent with those for NREM sleep.     

Intrakranielle Keimzelltumoren (Teratome und Seminome)

Zusammenfassung Die besonderen Erscheinungsformen intrakranieller Keimzellgeschwülste werden an 11 Fällen des Institutes für Pathologische Anatomie der Universität Zürich demonstriert. Bei 2 Fällen handelt es sich um reine Teratome verschiedenen Differenzierungsgrades, bei 8 Fällen um seminomartige Tumoren. Eine Geschwulst ist als Kombination eines Teratoms mit einem Seminom aufzufassen. Bei einem der 8 Patienten mit rein seminomartigen Tumoren bestand als Besonderheit eine multizentrische seminomartige Geschwulst in der Suprasellärgegend und im Mediastinum. Die histologischen Bilder der verschiedenen intrakraniellen Keimzellgeschwülste und die relative Häufigkeit der einzelnen Tumorformen entsprechen weitgehend denjenigen gleichartiger Geschwülste des Hodens. Die Tumoren lassen sich deshalb ohne Schwierigkeiten nach dem Klassifikationsschema für Hodengeschwülste von Collins und Pugh einordnen. Die seminomartigen intrakraniellen Geschwülste sind mit dem anisomorphen Pinealom von Zülch identisch. Die kleinzellige Komponente derartiger Tumoren ist als entzündliche Reaktion zu interpretieren, zeigt sie doch die gleichen Erscheinungsformen wie bei den Seminomen des Hodens. Die Intensität der entzündlichen Reaktion scheint gewisse Rückschlüsse auf die Malignität der Geschwülste zu erlauben.

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Intracranial germ cell tumors (teratomas and seminomas)

Summary The special problems of intracranial germ cell tumors are demonstrated and discussed with reference to a series of 11 cases from the Institute of Pathological Anatomy of the University of Zürich. 2 cases had pure teratomas varying in the degree of differentiation, 8 had seminoma-like tumors, and in 1 case there was a mixture of seminoma-like tumor and teratoma. One of the eight cases with seminoma-like tumor showed a multicentric seminoma-like tumor partly in the suprasellar region, partly in the mediastinum. The histological pattern of intracranial germ cell tumors and their relative frequency are in keeping with those of such tumors in the testes. Therefore, the classification of Collins and Pugh can be applied without difficulty. The seminoma-like intracranial tumors are identical to the anisomorphic pinealoma described by Zülch. The small cell component of the tumor is thought to be an inflammatory reaction and shows the same pattern as in seminoma of the testis. The intensity of the inflammation, especially the epitheloid cell reaction, may be related to the malignancy of the tumor.