Effects of Prolonged Depolarization on the Nicotinic Acetylcholine Receptors of PC12 Cells

Abstract

To determine whether prolonged depolarization and/or changes in intracellular Ca2+ concentrations stimulate adaptive responses of neuronal nicotinic acetylcholine receptors, PC12 pheochromocytoma cells were grown in medium containing various concentrations of K+. Nicotinic receptor function was determined as carbachol-stimulated uptake of 86Rb+. Cells were exposed to 50 mM K+ for up to 4 days and then allowed to repolarize for 60 min. Under these conditions, no changes in basal or carbachol-stimulated uptake of 86Rb+ were observed. Furthermore, neither the time course of carbachol-stimulated uptake or the carbachol concentration dependence of 86Rb+ uptake was altered. Finally, concurrent depolarization did not affect the functional down-regulation produced by chronic exposure of the cells to carbachol. Thus, neuronal nicotinic acetylcholine receptors on PC12 cells do not appear to be regulated by depolarization or prolonged elevation of the intracellular Ca2+ level.

The Magnitude of α7 Nicotinic Receptor Currents in Rat Hippocampal Neurons Is Dependent upon GABAergic Activity and Depolarization

“…The relationship between depolarization-induced up-regulation of ␣-bungarotoxin binding sites and changes in receptor-channel function remained mostly untested or unproven in previous studies (DeLorme and McGee, 1988;Smith et al, 1983;Geertsen et al, 1988). One study did show an increased receptor-mediated Ca 2ϩ influx in GH 4 C 1 rat pituitary cells stably expressing rat ␣7 receptors exposed to 50 mM K ϩ for 2 to 3 days, without changes in agonist potency (Quik et al, 1997).…”

“…However, TTX reduces the number of detectable ␣7* nAChR clusters only in a subpopulation of GABAergic neurons in the mixed hippocampal cultures, whereas total ␣-bungarotoxin binding is in fact unchanged (Kawai et al, 2002). Furthermore, none of these previous studies evaluated the effect of depolarization on ␣7* receptor activity directly through ion channel current measurements, and those that used functional assays failed to demonstrate any corresponding change in responses mediated by ␣7* nAChRs (DeLorme and McGee, Jr., 1988;Betz, 1983;Smith et al, 1983;Geertsen et al, 1988;De Koninck and Cooper, 1995;Quik et al, 1997;Ridley et al, 2002).…”

“…Treatment with KCl for several days leads to membrane depolarization and sustained calcium influx mediated by voltage-dependent Ca 2ϩ channels (VDCC), as demonstrated in cultured rat sympathetic neurons (Koike and Tanaka, 1991). The effect of high K ϩ has been studied in several cell types expressing native ␣7* receptors in culture (DeLorme and McGee, Jr., 1988;Betz, 1983;Smith et al, 1983;Geertsen et al, 1988Geertsen et al, , 1992De Koninck and Cooper, 1995;Ridley et al, 2002), including hippocampal neurons (Ridley et al, 2001), and also in cells transfected with the ␣7 gene (Quik et al, 1996(Quik et al, , 1997. In these diverse models, treatment with 20 to 50 mM KCl for 1 to 7 days consistently leads to increased ␣7 transcript levels and/or ␣-bungarotoxin binding sites.…”

Single Cells as Biosensors for Chemical Separations

“…Information on the presence or absence of a species (above some concentration limit) can be achieved rapidly with high sensitivity and selectivity. Quantitative assessment of analyte concentration should prove feasible for species that evoke graded responses over some concentration range (27,28). In many instances, however, variability in the response between cells may necessitate numerous separations to generate accurate dose-response relations.…”