L‐type calcium channel activity regulates sodium channel levels in rat pituitary GH3 cells

Abstract

The effects of chronic pharmacological modulation of L‐type Ca2+ channel activity on the cell surface expression of Na+ channels were examined in GH3 cells. Prolonged inhibition (4–5 days) of L‐channels with nimodipine caused a 50–60 % decrease in the peak amplitude of whole‐cell Na+ currents recorded with the patch‐clamp technique. On the contrary, prolonged exposure to the L‐channel agonist Bay K 8644 induced an ≈2.5‐fold increase in peak Na+ current. In both cases, there were only minor changes in cell capacitance and no significant changes in Na+ channel gating properties. Measurements of the specific binding of radiolabelled saxitoxin to intact cells showed that nimodipine treatment reduced the number of cell surface Na+ channels, whereas treatment with Bay K 8664 produced the opposite effect. The dual regulation of Na+ channel abundance explained the mentioned changes in Na+ current amplitude. Plasma membrane Na+ channels had a half‐life of ≈17 h both in control cells and in cells treated with Bay K 8644, as estimated from the rate of decay of peak Na+ current after inhibition of protein synthesis with cycloheximide. Actinomycin D, an inhibitor of gene transcription, and also cycloheximide, occluded the stimulatory effect of Bay K 8644 on Na+ current density when measured over a 24 h period. These findings indicate that the entry of Ca2+ through L‐type channels influences in a positive way the number of functional Na+ channels in GH3 cells, and suggest that Ca2+ influx stimulates either Na+ channel gene expression or the expression of a regulatory protein that promotes translocation of pre‐assembled Na+ channels into the plasma membrane.

Ion Channel Development, Spontaneous Activity, and Activity-Dependent Development in Nerve and Muscle Cells

“…Similar activity-dependent downregulation of Na ϩ channels occurs in skeletal and cardiac muscle cells (77,105,452,538), where there is direct evidence that the effects are secondary to Ca 2ϩ entry. Activity has been reported to upregulate Na ϩ channel density in a Ca 2ϩ -dependent manner in GH3 cells (417 (528). In DRG neurons, Ca 2ϩ currents show similar dependence on the specific patterns of stimulation as do other activity-regulated molecules (331).…”

Hedgehog and PI-3 kinase signaling converge on Nmyc1 to promote cell cycle progression in cerebellar neuronal precursors

“…Cycloheximide chase is an established method for assaying turnover of cell cycle regulatory proteins (Schmidt et al, 2002), including Myc (Lehr et al, 2003). We chose this method because it permits assessment of relative stability and protein turnover despite the limiting quantities of cells in primary neuronal cell cultures (Monjaraz et al, 2000). As shown (Fig.…”

Attenuation of Ketamine Effects by Nimodipine Pretreatment in Recovering Ethanol Dependent Men Psychopharmacologic Implications of the Interaction of NMDA and L-Type Calcium Channel Antagonists

“…A second possibility is that nimodipine modulated NMDA receptor function making NMDA receptors less available to ketamine blockade. Nimodipine, for example, reduces membrane depolarization through blockade of L-type VSCCs and, to a lesser extent, voltage-gated sodium channels (Monjaraz et al 2000). This effect would be predicted to reduce the number of NMDA receptors in the activated state (Yu and Salter 1998).…”