Biomedical subjects

D G Jugloff

Publications and source records attributed to D G Jugloff.

3 recordsLinked to original sources

PubMed2000

Internalization of the Kv1.4 potassium channel is suppressed by clustering interactions with PSD-95.

The contribution of voltage-dependent ion channels to nerve function depends upon their cell-surface distributions. Nevertheless, the mechanisms underlying channel localization are poorly understood. Two phenomena appear particularly important: the clustering of channels by membrane-associated guanylate kinases (MAGUKs), such as PSD-95, and the regional stabilization of cell-surface proteins by differential suppression of endocytosis. Could these phenomena be related? To test this possibility we examined the effect of PSD-95 on the internalization rate of Kv1.4 K(+) channels in transfected HEK293 cells using cell-surface biotinylation assays. When expressed alone Kv1.4 was internalized with a half-life of 87 min, but, in the presence of PSD-95, Kv1.4 internalization was completely suppressed. Immunochemistry and electrophysiology showed PSD-95 had little effect on total or cell-surface levels of Kv1.4 or on current amplitude, activation, or inactivation kinetics. Clustering was necessary and sufficient to suppress Kv1.4 internalization since C35S-PSD-95, a mutant reported to bind but not cluster Kv1.4, (confirmed by imaging cells co-expressing a functional, GFP-variant-tagged Kv1.4) restored and, surprisingly, enhanced the rate of Kv1.4 internalization (t((1)/(2)) = 16 min). These data argue PSD-95-mediated clustering suppresses Kv1.4 internalization and suggest a fundamentally new role for PSD-95, and perhaps other MAGUKs, orchestrating the stabilization of channels at the cell-surface.

Amino Acid Sequence↗

PubMed1997

Kainic acid-induced generalized seizures alter the regional hippocampal expression of the rat Kv4.2 potassium channel gene.

Potassium channels play a key role in the regulation of membrane excitability. We investigated the gene expression response of the Kv4.2 subtype of potassium channel, in the rat hippocampus, to a brief (5 min) episode of kainic acid-induced seizures. Our results demonstrate that Kv4.2 expression is reduced in the granule cell layer of the dentate gyrus at 3 h post-seizure, while no significant changes in expression are observed in other hippocampal subfields. At 6 h post-challenge, expression in both dentate hilar cells and granule cells is reduced, while no other significant changes are observed. At 24 h post-challenge, expression levels for Kv4.2 in the dentate granule cells have rebounded to levels greater than control, while expression levels are significantly reduced in the CA3 and CA4 subfields. No significant changes in Kv4.2 expression are observed in kainic acid-administered animals that fail to seize, indicating that the changes in gene expression result from seizure activity and not from the direct actions of the administered kainic acid. These results demonstrate that brief kainic acid-induced epileptiform activity promotes alterations in the expression levels for the Kv4.2 subtype of potassium channel gene.

Animals↗

PubMed1997

N-Type calcium channels in the developing rat hippocampus: subunit, complex, and regional expression.

The expression of multiple classes of voltage-dependent calcium channels (VDCCs) allows neurons to tailor calcium signaling to functionally discrete cellular regions. In the developing hippocampus a central issue is whether the expression of VDCC subtypes plays a role in key phases such as migration and synaptogenesis. Using radioligand binding and immunoblotting, we show that some N-type VDCCs exist before birth, consistent with a role in migration; however, most N-VDCC subunit expression is postnatal, coinciding with synaptogenesis. Immunoprecipitation studies indicate that the increased expression of N-VDCCs in early development occurs without subunit switching because there is no change in the fraction of beta3 subunits in the N-VDCC alpha1B-beta3 heteromers. Fluorescence imaging of cell surface N-VDCCs during this period reveals that N-VDCCs are expressed on somata before dendrites and that this expression is asynchronous between different subfields of the hippocampus (CA3-CA4 before CA1-CA2 and dentate gyrus). Our data argue that N-VDCC expression is an important cue in the genesis of synaptic transmission in discrete hippocampal subfields.

Animals↗