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M Klein

Publications and source records attributed to M Klein.

At least 721 records · Page 40Linked to original sources
PubMed1978

Presynaptic modulation of voltage-dependent Ca2+ current: mechanism for behavioral sensitization in Aplysia californica.

Behavioral sensitization of the gill-withdrawal reflex of Aplysia is the result of a prolonged increase in transmitter release from the presynaptic terminals of sensory neurons. Earlier work suggested that this presynaptic facilitation might be mediated by a serotonin-sensitive adenylate cyclase in the sensory neuron terminals. Here we present evidence that presynaptic facilitation results from a cyclic AMP-dependent increase in the calcium current that underlies action potentials in the sensory neurons. The action potentials of sensory neuron cell bodies have, in addition to a sodium current, a calcium current that is enhanced by blocking the opposing potassium current with tetraethylammonium. Under these conditions, the action potentials show a slowly repolarizing plateau that follows the Nernst potential for a calcium electrode and serves as a sensitive assay for changes in calcium current. Stimulation of the pathway that mediates sensitization, incubation with serotonin or phosphodiesterase inhibitors, or intracellular injection of cyclic AMP produces an increase in the calcium plateau in the presence of tetraethylammonium. In addition, both before and after sensitizing stimulation, the duration of the plateau potential parallels transmitter release as measured by the amplitude of monosynaptic excitatory postsynaptic potentials evoked in the motor neurons by intracellular stimulation of single sensory neurons. These results are consistent with the idea that presynaptic facilitation is caused by a cyclic AMP-mediated increase in a voltage-sensitive calcium current in sensory neuron presynaptic terminals. This synaptic action is novel in that it can produce little or no change in the resting potential, is of long duration, and exerts its influence directly on a conductance triggered by the action potential, rather than on non-voltage-sensitive conductances, as is typical of conventional synaptic actions.

Action Potentials↗
PubMed1978

A graphic approach to assessing interrelationships among minute ventilation, arterial carbon dioxide tension, and ratio of physiologic dead space to tidal volume in patients on respirators.

A graphic analysis of the relationships among minute ventilation, arterial PCO2, and the ratio of physiologic dead space to tidal volume is presented for the bedside clinical evaluation of patients receiving continuous respiratory support. With simultaneous measurement of minute ventilation and arterial PCO2, the graph can be used to determine the patient's ratio of dead space to tidal volume. This information can subsequently be used (1) for respirator adjustments to obtain the desired arterial PCO2; (2) to assess the severity of ventilation/perfusion unevenness; and (3) to follow the patient's response to respiratory therapy. It provides the clinician with a conceptual tool with which he can assess the status of a patient's gas exchange and more accurately evaluate and plan his course of treatment.

Carbon Dioxide↗
PubMed1978

Pretrial commitment.

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Commitment of Persons with Psychiatric Disorders↗
PubMed1978

[Changes in the masticatory system in myasthenia gravis].

Myastenia gravis causes by a hypofunction of the striated musculature a variable motor dyscoordination, which was examined in 106 patients. Hypofunction alone does not have any periodontal consequences, caries intensity however was obvious. Incoordination caused by hypofunction often is the cause for TMJ damage. The increase in mouth opening and of masticating force by Tensilon therapy is a characteristic and diagnostically useful test for myasthenia patients.

Dental Caries↗
PubMed1977

Thermodynamic and conformational studies on an immunoglobulin light chain which reversibly precipitates at low temperatures.

A lambda light chain, isolated from an immunoglobulin G molecule, was found to reversibly precipitate at low temperatures. This cryoprecipitation was a function of pH, ionic strength, protein concentration, and time as well as temperature. The lambda chain underwent a cooperative conformational change as the temperature was lowered from 26 to 0 degrees C as judged by ultraviolet difference spectroscopy and circular dichroism. Normal lambda chains showed no conformational change. By difference spectroscopy it was possible to calculate the equilibrium constant governing the conformational change. The change was strongly exothermic (delta H approximately -80 kcal mol-1) and accompanied by a large decrease in entropy (delta S approximately -280 eu). The midpoint of the transition was dependent on the initial protein concentration, suggesting that only the noncovalent dimer of the lambda chain exhibited the conformational change. The existence of a monomer-dimer eqiulibrium (KA approximately 4 X 10(5) M-1) was confirmed by sedimentation velocity. No conformational change was observed by circular dichroism at concentrations where greater than 95% of lambda chain was in the form of a monomer. Although high ionic strength inhibited cryoprecipitation, it had no effect on the conformational change. Stabilization of the dimer by forming an interchain disulfide bond between two monomers abolished both the conformational change and cryoprecipitation. A fragment corresponding to the constant region was isolated from both peptic and tryptic digests of the lambda chain. This fragment neither cryoprecipitated nor showed temperature dependence conformational changes. It proved impossible to isolate a fragment corresponding to the variable region. Both qualitative and quantitative models are presented to account for the behavior of the lambda chain at low temperatures.

Humans↗
PubMed1977

Single cutaneous plasmacytoma with crystalloid inclusions.

A patient had a primary cutaneous plasmacytoma of the cheek. Histologic studies showed dense aggregates of plasma cells admixed with occasional histiocytes. The cytoplasm of the histiocytes contained needle-like structures. Electron microscopy showed these structures to be completely enclosed within smooth membranes. They often were rhombic, with occasional broken-off corners. It is hypothesized that these structures represent protein that has been secreted by the plasma cells and subsequently phagocytosed and stored in crystalloid form by the neighboring histiocytes. The patient is asymptomatic 1 1/2 years after removal of the tumor.

Cheek↗