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1999) identified electroneutral K-Cl cotransporter in the slowly adapting stretch receptor neurone of the European lobster. The experiments were based on microelectrode techniques. This allowed us to perform steady-state measurements of the so-called "instantaneous" current-voltage relationships (around a holding voltage of -65 mV after a blockage of the cell's action potential and hyperpolarization-activated currents) and intracellular ion concentrations at various settings of the extracellular K(+) and Cl(-) concentrations. From the results
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Experiments were performed to define quantitatively the substrate (K(+) and Cl(-)) dependence of the transport function (production of equally large and oppositely directed K(+)and Cl(-) flows/currents) of an earlier (Theander et al
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Local Lyapunov Vectors
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Neurosciences
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all membrane currents add up to zero. For the cotransporter currents
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and (b) enabling rapid transmembrane K(+) shifts that provide for a stabilization of the cell's membrane voltage and membrane excitability in cases of varying extracellular K(+) concentrations. The model predictions gave
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current restrai
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in steady state
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no clear evidence that the K-Cl cotransporter is critically involved in the cell's volume regulation in conditions of varying extracellular osmolalities
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the model predictions suggested that the K-Cl cotransporter does play an important role in (a) keeping intracellular Cl(-) low for a proper function of the cell's inhibitory system
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the negative sums of the inferred non-KCl cotransporter K(+) and Cl(-) currents could be taken as equivalents of the K-Cl cotransporter's K(+) and Cl(-) currents for the reason that
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this relationship could be reproduced by a Hill function-based enzyme kinetic expression simulating inward and outward transmembrane electroneutral ion transports. Following insertion of this expression into a comprehensive model of electrical membrane functions and intracellular solute and solvent control in the lobster stretch receptor neurone
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thus inferred for a range from 2.5/410.5 to 40.0/448.0 mM external K(+)/Cl(-)
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to about 20 nA cell(-1) at the highest external K(+)/Cl(-) concentrations. Formally
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we could then define steady-state values of all of the cell's non-KCl cotransporter K(+) and Cl(-) currents. Finally
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we found that their absolute values increased in a nonlinear fashion from about 5 nA cell(-1) at the lowest
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