The temperature dependence of conductance of the sodium channel: implications for mechanisms of ion permeation.

Voltage-gated sodium channel currents were recorded in cell-attached and inside-out membrane patches from rat ventricular myocytes at temperatures ranging from 4 degrees C to 36 degrees C. The effects of changes in temperature on channel conductance were accurately determined using a digital signal processing technique based on hidden Markov models. We show that the cardiac sodium channel has multiple conductance levels, with the most frequently observed sublevel being either 11 pS or 22 pS at room temperature in 280 mM Na+, depending on the dissociation procedures adopted. The single channel current-voltage relationship is ohmic at all of the temperatures studied. The conductance increases steeply with temperature, with Q10 ranging from 1.4 to 1.5. The proportional change in channel conductance with increasing temperature was greater than the corresponding change in bulk conductivity of electrolyte solutions, suggesting that an ion traversing the channel needs to surmount a small additional energy barrier. An activation energy deduced from a plot of the logarithm of single channel conductance against the inverse of temperature is about 28 kJ mole-1. We provide one possible interpretation of the observed conductance-temperature relationship in terms of the details of the microscopic interactions operating between the protein wall, ions and water molecules.

Sensory and affective predictors of overall pain and emotions associated with affective pain.

OBJECTIVE: Psychological scaling techniques consistently produce separate ratings for sensory and affective components of pain. This study examines the relative contributions of these components to pain as a whole and the contributions of different emotions to the affective component of pain. DESIGN: The design was correlational. Visual analogue scales were used to quantify overall pain, sensory pain, affective pain, and individual emotions. These data lent themselves to regression techniques for expressing pain as a function of sensation and affect as a function of emotion types. SETTING: Data were collected at the Pain Clinic within the Department of Physical Medicine at the Ohio State University. PATIENTS: Subjects were 40 chronic pain sufferers admitted to an inpatient pain management program. RESULTS AND CONCLUSIONS: Ratings of overall pain were not a simple summation of sensory and affective ratings, but a linearly additive function of both component ratings each with a unique weighting. The affective component of pain was a function of three differentially weighted sets of emotions, anger, fear, and sadness being most salient. Implications arise for the broader assessment of chronic pain and the treatment of specific emotions that may be particularly associated with the pain.

Synthesis, photochemistry, and biological activity of a caged photolabile acetylcholine receptor ligand.

A biologically inert photolabile precursor of carbamoylcholine has been synthesized; it is photolyzed to carbamoylcholine, a well-characterized acetylcholine analogue, with a half-time of 40 microseconds at pH 7.0 and a quantum yield of 0.8. The compound, N-(alpha-carboxy-2-nitrobenzyl)carbamoylcholine, was synthesized from (2-nitrophenyl)glycine. The photolysis rates (of five compounds) and the biological activity (of two compounds) were determined, and both properties were found to depend on the nature of the substituents on the photolabile protecting group. Laser pulse photolysis at wavelengths between 308 and 355 nm was used to investigate the wavelength dependence, quantum yield, and rate of the photolysis reaction. Photolysis products were isolated by high-performance liquid chromatography and identified by chemical and spectroscopic analysis and by their ability to activate the nicotinic acetylcholine receptor. BC3H1 muscle cells containing those receptors and a cell-flow method were used in the biological assays. The approach described may be useful in the preparation and characterization of other photolabile precursors of neurotransmitters that contain amino groups. The importance of these rapidly photolyzed, inert precursors of neurotransmitters is in chemical kinetic investigations of the reactions involving diverse neuronal receptors; such studies have been hampered because the available techniques have an insufficient time resolution.