The malonyl gramicidin channel: NMR-derived rate constants and comparison of calculated and experimental single-channel currents

1980 ◽  
Vol 55 (1) ◽  
pp. 29-51 ◽  
Author(s):  
D. W. Urry ◽  
C. M. Venkatachalam ◽  
A. Spisni ◽  
R. J. Bradley ◽  
T. L. Trapane ◽  
...  
Keyword(s):  
Rate Constants ◽  
Single Channel ◽  
Gramicidin Channel ◽  
Single Channel Currents ◽  
Channel Currents

scholarly journals Rate theory calculation of gramicidin single-channel currents using NMR-derived rate constants.

1980 ◽  
Vol 77 (4) ◽  
pp. 2028-2032 ◽  
Author(s):  
D. W. Urry ◽  
C. M. Venkatachalam ◽  
A. Spisni ◽  
P. Lauger ◽  
M. A. Khaled
Keyword(s):  
Rate Constants ◽  
Single Channel ◽  
Rate Theory ◽  
Single Channel Currents ◽  
Theory Calculation ◽  
Channel Currents

scholarly journals Activation of Torpedo acetylcholine receptors expressed in mouse fibroblasts. Single channel current kinetics reveal distinct agonist binding affinities.

1990 ◽  
Vol 96 (2) ◽  
pp. 395-437 ◽  
Author(s):  
S M Sine ◽  
T Claudio ◽  
F J Sigworth
Keyword(s):  
Rate Constants ◽  
Single Channel ◽  
Fibroblast Cell ◽  
Mouse Fibroblast ◽  
Parameter Estimates ◽  
Agonist Binding ◽  
Extracellular Solution ◽  
Experimental Conditions ◽  
Single Channel Currents ◽  
Channel Currents

The experiments described examine single channel currents recorded through Torpedo acetylcholine receptor channels stably expressed by a mouse fibroblast cell line. Closed-duration histograms were constructed from currents elicited by 0.5-300 microM acetylcholine (ACh). The concentration dependence of closed durations is well described by a four-state linear scheme with the addition of open-channel block by ACh. Analysis of closed durations measured at low concentrations gives estimates of the rate of opening of doubly liganded receptors, beta, the rate of dissociation of ACh from doubly liganded receptors, k-2, and the rate of channel closing, alpha. The rate of ACh dissociation from singly liganded receptors, k-1, is then deduced from closed-duration histograms obtained at intermediate ACh concentrations. With k-1, k-2 and beta determined, the rates of ACh association, k+1 and k+2, are estimated from fitting closed-duration histograms obtained over a range of high ACh concentrations. A complete set of rate constants is presented for three experimental conditions: (a) Ca2(+)-free extracellular solution containing 1 mM free Mg2+ at 22 degrees C, (b) Ca2(+)-free solution at 12 degrees C, and (c) extracellular Ca2+ and Mg2+, both at 0.5 mM, at 22 degrees C. For all three conditions the dissociation constant for the first agonist binding site is approximately 100-fold lower than that for the second site. The different affinities are due primarily to different dissociation rates. Both the association and dissociation rates depend strongly on temperature. At 22 degrees C ACh associates at diffusion-limited rates, whereas at 12 degrees C association is 30- to 60-fold slower. Also slowed at 12 degrees C are beta (4-fold), k-2 (3-fold), k-1 (25-fold), and alpha (15-fold). In contrast to the activation rate constants, those for ACh-induced block decrease only twofold between 22 and 12 degrees C. Changing from a Ca2(+)-free to a Ca2(+)-containing extracellular solution does not affect k+1 and k+2, but increases beta (twofold) and decreases k-2, k-1, and alpha (all twofold). Spectral analysis of single channel currents supports the parameter estimates obtained from fitting the open- and closed-duration histograms, and improves resolution of brief channel blockages produced by ACh.

A Calcium-Activated Nonspecific Cation Channel from Olfactory Receptor Neurones of the Silkmoth Antheraea Polyphemus

1991 ◽  
Vol 161 (1) ◽  
pp. 455-468
Author(s):  
F. ZUFALL ◽  
H. HATT ◽  
T. A. KEIL
Keyword(s):  
Olfactory Receptor ◽  
Single Channel ◽  
Membrane Vesicles ◽  
Cation Channel ◽  
Voltage Response ◽  
Antheraea Polyphemus ◽  
Cell Excitability ◽  
Olfactory Receptor Neurones ◽  
Single Channel Currents ◽  
Channel Currents

Single-channel patch-clamp techniques were used to identify and characterize a Ca2+-activated nonspecific cation channel (CAN channel) on insect olfactory receptor neurones (ORNs) from antennae of male Antheraea polyphemus. The CAN channel was found both in acutely isolated ORNs from developing pupae and in membrane vesicles from mature ORNs that presumably originated from inner dendritic segments. Amplitude histograms of the CAN single-channel currents presented well-defined peaks corresponding to at least four channel substates each having a conductance of about 16 pS. Simultaneous gating of the substates was achieved by intracellular Ca2+ with an EC50 value of about 80 nmoll−1. Activity of the CAN channel could be blocked by application of amiloride (IC50 <100nmoll−1). Moreover, in the presence of 1μmoll−1 Ca2+, opening of the CAN channel was totally suppressed by 10 μmoll−1 cyclic GMP, whereas ATP (1 mmol l−1) was without effect. We suggest that the CAN channel plays a specific role in modulation of cell excitability and in shaping the voltage response of ORNs.

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