Rates and equilibria at the acetylcholine receptor of electrophorus electroplaques. A study of neurally evoked postsynaptic currents and of voltage-jump relaxations

Kinetic measurements are employed to reconstruct the steady-state activation of acetylcholine [Ach] receptor channels in electrophorus electroplaques. Neurally evoked postsynaptic currents (PSCs) decay exponentially; at 15°C the rate constant, α, equals 1.2 ms^(-1) at 0 mV and decreases e-fold for every 86 mV as the membrane voltage is made more negative. Voltage-jump relaxations have been measured with bath-applied ACh, decamethonium, carbachol, or suberylcholine. We interpret the reciprocal relaxation time 1/τ as the sum of the rate constant α for channel closing and a first-order rate constant for channel opening. Where measureable, the opening rate increases linearly with [agonist] and does not vary with voltage. The voltage sensitivity of small steady-state conductances (e- fold for 86 mV) equals that of the closing rate α, confirming that the opening rate has little or no additional voltage sensitivity. Exposure to α-bungarotoxin irreversibly decreases the agonist-induced conductance but does not affect the relaxation kinetics. Tubocurarine reversibly reduces both the conductance and the opening rate. In the simultaneous presence of two agonist species, voltage-jump relaxations have at least two exponential components. The data are fit by a model in which (a) the channel opens as the receptor binds the second in a sequence of two agonist molecules, with a forward rate constant to 10^(7) to 2x10^(8) M^(-1)s^(-1); and (b) the channel then closes as either agonist molecule dissociates, with a voltage-dependent rate constant of 10^(2) to 3x10^(3)s^(-1)

Functional Stoichiometry at the Nicotinic Receptor. The Photon Cross Section for Phase 1 Corresponds to Two Bis-Q Molecules per Channel

These experiments examine changes in the agonist-induced conductance that occur when the agonist-receptor complex is perturbed. Voltage-clamped Electrophorus electroplaques are exposed to the photoisomerizable agonist trans-Bis-Q A 1-µs laser flash photoisomerizes some trans-Bis-Q molecules bound to receptors; because the cis configuration is not an agonist, receptor channels close within a few hundred microseconds. This effect is called phase 1. We compare (a) the fraction of channels that close during phase 1 with (b) the fraction of trans-Bis-Q molecules that undergo trans → cis photoisomerization. Parameter a is measured as the fractional diminution in voltage-clamp currents during phase 1. Parameter b is measured by changes in the optical spectra of Bis-Q solutions caused by flashes . At low flash intensities, a is twice b, which shows that the channel can be closed by photoisomerizing either of two bound agonist molecules. Conventional dose-response studies with trans-Bis-Q also give a Hill coefficient of two. As a partial control for changes in the photochemistry caused by binding of Bis-Q to receptors, spectral measurements are performed on the photoisomerizable agonist QBr, covalently bound to solubilized acetylcholine receptors from Torpedo. The bound and free agonist molecules have the same photoisomerization properties. These results verify the concept that the open state of the acetylcholine receptor channel is much more likely to be associated with the presence of two bound agonist molecules than with a single such molecule

Conductance increases produced by bath application of cholinergic agonists to Electrophorus electroplaques

When solutions containing agonists are applied to the innervated face of an Electrophorus electroplaque, the membrane's conductance increases. The agonist-induced conductance is increased at more negative membrane potentials. The "instantaneous" current-voltage curve for agonist-induced currents is linear and shows a reversal potential near zero mV; chord conductances, calculated on the basis of this reversal potential, change epsilon-fold for every 62-mV change in potential when the conductance is small. Conductance depends non- linearly on small agonist concentrations; at all potentials, the dose-response curve has a Hill coefficient of 1.45 for decamethonium (Deca) and 1.90 for carbamylcholine (Carb). With agonist concentrations greater than 10^(-4) M Carb or 10^(-5) M Deca, the conductance rises to a peak 0.5-1.5 min after introduction of agonist, then declines with time; this effect resembles the "desensitization" reported for myoneural junctions. Elapid alpha-toxin, tubocurarine, and desensitization reduce the conductance without changing the effects of potential; the apparent dissociation constant for tubocurarine is 2 X 10^(-7) M. By contrast, procaine effects a greater fractional inhibition of the conductance at high negative potentials

Electrodeposited nanoparticles: properties and photocatalytic applications

The work presented in this thesis reports on fundamental studies into electrodeposition of gold and silver nanoparticulate spheroids on a conducting substrate, Fluorine-doped tin-oxide, and the manipulation of the electrodeposition conditions in order to influence and control the size and surface concentration of spheroids. Methods to control the deposition included chemical modification of the surface with an adsorbed monolayer of 3-aminopropyldimethylmethoxysilane, and manipulation of the potential pulse scheme, especially using a double pulse 'nucleation and growth' approach. The optimised method for production of silver and gold nanoparticulate surfaces was utilised to selectively create surfaces that yield strong surface enhanced Raman scattering (SERS) enhancements, as well as metal enhanced fluorescence. These enhancements have been quantified using the probe molecules Trans-1,2-bis(4-pyridyl)ethylene (BPE) and [Os(bpy)2Qbpy]2+ respectively (where bpy is 2,2’-bipyridyl and Qbpy is 2,2’:4,4’’:4’4’’-quarterpyridyl). Spontaneously formed, densely packed monolayers of [Os(bpy)2PIC]2+ have been formed on fluorine-doped tin-oxide (FTO) electrodes, and films of [Os(bpy)2Qby]2+ have been formed on silver nanoparticulate decorated FTO (where bpy is 2,2’-bipyridyl, PIC is 2-(4-carboxyphenyl)imidazo[4,5- f][1,10]phenanthroline, and Qbpy is 2,2’:4,4’’:4’4’’-quarterpyridyl). The quenching mechanism of the polyoxotungstate anion α-[S2W18O62] (POW) on the two osmium polypyridyl complexes in solution has been identified by analysis of the Stern-Volmer plots. The quenching of monolayers of these complexes by POW, coupled to the electrochemical regeneration of the ground state osmium complex by potential application at the FDTO electrode, has been used to photo-catalytically reduce methyl viologen. Finally a wireless gold bipolar electrode in a microchannel, whose potential is floating and managed by exerting potential control over the electrolyte solution rather than individual electrodes, has been used as the basis for an electrochemiluminescent DNA microsensor. The function of the DNA microsensor has been optimised to maximise signal intensity by altering the ECL solution, and by manipulating the pathway by which the ECL reaction proceeds. DNA binding has been detected based on catalysis of the oxygen reduction reaction (ORR) at (DNA linked) platinum nanoparticles. The ORR can be replaced with other reduction reactions to detect other species such as anthraquinones. The possibility of using this device for quantitative sensing of both DNA and other species is discussed

Theories of Reading and Implications for Teachers

When reading current research, one is overwhelmed by the proliferation of new theories of the reading process. The purpose of this paper is to present the prevailing theories of reading comprehension, to examine their similarities and differences, and determine whether they are distinctly different or represent a general theory of cognitive development specifically applied to reading

Reading Disabilities: Are There Fewer In Japan?

Comparative reading research offers us an avenue to study a universal process — learning to read — in cultures and societies with different customs, traditions and writing systems. Such studies provide insights into how we learn, and fail to learn, and information about methods for meeting the reading needs of different students in our own country. In studying learning to read in another writing system there is always the temptation to make comparisons in terms of which is better or worse, easier or harder. In the past, research from Japan indicated that learning to read in Japanese produced fewer reading disabilities due to its writing system. Both past and more recent research on comparative differences in reading disabilities, particularly in Japan, have been examined to determine whether in fact more recent findings corroborate these beliefs

Study of aerodynamic technology for single-cruise-engine VSTOL fighter/attack aircraft, phase 1

A conceptual design and analysis on a single engine VSTOL fighter/attack aircraft is completed. The aircraft combines a NASA/deHavilland ejector with vectored thrust and is capable of accomplishing the mission and point performance of type Specification 169, and a flight demonstrator could be built with an existing F101/DFE engine. The aerodynamic, aero/propulsive, and propulsive uncertainties are identified, and a wind tunnel program is proposed to address those uncertainties associated with wing borne flight