Biomedical subjects

G Jeserich

Publications and source records attributed to G Jeserich.

At least 19 recordsLinked to original sources

PubMed2002

Small conductance calcium-activated potassium channels of trout CNS: molecular structure, developmental expression, and partial biophysical characterization.

Two small conductance calcium-activated potassium channels that exhibited amino acid similarity with mammalian SK2 and SK3, respectively, were PCR cloned from the CNS of trout and sequenced. Upon heterologous expression in Sf21 insect cells trout SK2 (termed tSK2) produced a calcium-dependent, voltage-insensitive, and non-inactivating current with a single unit conductance of about 11 pS. This current was half maximally activated by 0.76 microM Ca(2+) and blocked by picomolar concentrations of apamin but not by TEA. Transcripts of both SK-related channels possessed a widespread distribution in the mature brain tissue of trout and outside the nervous system were detectable in muscle tissue as well as in liver. As revealed by RT-PCR analysis transcripts encoding tSK2 and tSK3 channels were early detectable during brain development (stage 30, shortly after hatching).

Animals↗

PubMed2001

Structure, heterologous expression, and adhesive properties of the P(0)-like myelin glycoprotein IP1 of trout CNS.

The IP1 protein of trout CNS myelin as well as an IP1/P(0) chimeric protein were stably expressed in CHO cells. Successful targeting of the recombinant proteins to the membrane surface was verified by immunofluorescence staining. Full-length expression of IP1 could be confirmed by Western blot analysis of proteins extracted from stably transfected CHO-cells. The adhesive properties of IP1 were studied by an in vitro aggregation assay in which microscopic examination was combined with electronic particle counting. While IP1 conveyed only a weak increase in cell aggregation of transfected CHO cells, the IP1/P0 chimera was much more effective. In the presence of specific antibodies, cell aggregation was strongly reduced. The adhesive properties of P(0)-like proteins are discussed considering recent crystallographic data on the atomic structure of the extracellular domain of mammalian P(0).

Amino Acid Sequence↗

PubMed2000

Voltage-gated potassium channels in retinal ganglion cells of trout: a combined biophysical, pharmacological, and single-cell RT-PCR approach.

Retinal ganglion cells of young mature trout were acutely isolated by tissue printing and analyzed with the whole-cell mode of the patch-clamp technique in combination with single-cell RT-PCR. All cells either exhibited spontaneous spiking activity or could be induced to fire trains of action potentials by current injection. Depolarizing voltage steps elicited a TTX-sensitive sodium inward current and a complex outward current that could be subdivided into a calcium-dependent component that was sensitive to 100 nM iberiotoxin as well as three major types of voltage-sensitive currents: 1) a high-threshold (-20 mV) noninactivating current that was highly sensitive to submicromolar TEA and quinine, resembling recombinant mammalian Kv3.1 channels; 2) a low-threshold DTX-sensitive current, matching mammalian Kv1; and 3) a fast-inactivating transient current that was highly sensitive to TEA (3 mM) but resistant to alpha-DTX (1 microM) and quinine (0.1 mM). By multiplex single-cell RT-PCR, coexpression of multiple transcripts encoding Shaker-related channel genes of trout (termed Tsha1-Tsha4) as well as two Shaw-related channels (termed Traw1 and Traw2) could be demonstrated in individual cells.

Action Potentials↗

PubMed2000

Molecular cloning and functional characterization of Shaw-related potassium channels of trout CNS.

Two Shaw-related potassium channels expressed in the CNS of trout were PCR cloned and sequenced: Traw1 was identified as a fish homologue to mammalian K(v)3.1, while Traw2 could not be exactly classified. Upon heterologous expression Traw1 exhibited a high threshold (-20 mV) non-inactivating delayed rectifier current that was efficiently blocked by submicromolar concentrations of TEA, 4-AP and quinine but not by alpha-DTX or apamin. The amplitude of the Traw1 induced current was reduced by the phorbol ester TPA, the effect being prevented by the proteinkinase inhibitor H7. Transcripts of both Shaw- related channels possess a widespread distribution in the mature brain tissue and outside the nervous system are detectable in muscle but not in liver. During brain development Traw1 mRNA was initially identified at stage 31 (shortly after hatching) while transcripts encoding Traw2 were detectable already at stage 28 (1 week before hatching).

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed2000

Isolation and heterologous expression of two genomic clones encoding Shaker-related potassium channels of trout CNS.

Two Shaker-related potassium channel genes (termed tsha1 and tsha2) expressed in the CNS of trout were cloned and sequenced. The coding regions of both genes were not interrupted by introns and exhibited a high overall sequence similarity to other members of the Shaker subfamily. By computer-assisted sequence alignments, tsha1 was identified as a fish homologue to the mammalian Kv1.2 subtype of potassium channels, whereas tsha2 did not show a preferential sequence homology but shared a uniform similarity to Kv1.1, Kv1.2, and Kv1.3. Upon heterologous expression in a mammalian glial cell line, both channels exhibited delayed rectifier current properties that differed from each other by their threshold potentials of activation and their pharamcological features: wheras the tsha1-mediated current was efficiently blocked by submicromolar concentrations of alpha-DTX but not by TEA, tsha2 was highly TEA-sensitive, correlating well with differences in the amino acid structure of the pore outer mouth region. As revealed by RT-PCR, Shaker-related potassium channels were sequentially expressed during trout brain development: tsha2 was found initially at stage 34, followed by tsha1 at stage 36, whereas two other members of the Shaker family (tsha3 and tsha4) were detectable much earlier (stage 30, hatching). In the mature brain tissue, no regional specialization of Shaker channel subtype expression was noted.

Amino Acid Sequence↗

PubMed1999

Voltage-gated sodium and potassium channels in radial glial cells of trout optic tectum studied by patch clamp analysis and single cell RT-PCR.

Radial glial cells in the visual center of trout were analyzed immunocytochemically and with the whole cell mode of the patch-clamp technique in combination with RT-PCR. By immunostaining with anti-GFAP antibodies radially oriented cell processes spanning the entire width of the tectum were brightly labeled, while with anti-S-100 antiserum the cell bodies residing in a discrete layer close to the ventricular border became most clearly visible. Virtually all radial glial cells examined in brain slices exhibited voltage-gated sodium inward currents that were activated above -40 mV, blocked by micromolar concentrations of TTX and totally eliminated if sodium was substituted for Tris in the bath solution. In contrast with adjacent nerve cells of the same slices radial glial cells did not exhibit spontaneous electrical activity and could not be stimulated to generate action potentials by depolarizing current injections. Two types of voltage-gated potassium outward currents were elicited by depolarizing voltage steps: a sustained current with delayed rectifier properties and a superimposed transient "A"-type current, both being activated at a threshold potential of -40 mV. In cultured radial glial cells subtle differences were noticed regarding current density, inactivation kinetics, and TEA-sensitivity of the potassium currents. Inwardly rectifying potassium currents activating at hyperpolarized voltages were not observed. By single cell RT-PCR the transcripts of two shaker-related potassium channel genes (termed tsha1-a fish homologue to Kv1.2- and tsha3) were amplified, while transcripts for tsha 2 and tsha 4 were not detected.

Animals↗

PubMed1998

Molecular structure and expression of shaker type potassium channels in glial cells of trout CNS.

Two shaker-related potassium channel transcripts (tsha1, tsha2) were identified in glial cells of trout central nervous system (CNS) by polymerase chain reaction (PCR)-cloning and sequencing. While tsha1 was highly similar to the mammalian Kv1.2 subtype of potassium channels, tsha2 did not show a preferential sequence homology with a particular subtype of shaker, but exhibited uniform similarity with mammalian Kv1.1, Kv1.2, and Kv1.3, respectively. Transcripts for the shaw and shal subfamilies of voltage-gated potassium channels were detected in whole brain tissue only but not in freshly dissociated glial cells. Using mRNA extracted from different glial cell types in combination with sequence specific PCR primers, tshal was found restricted to oligodendrocytes and their progenitor cells, while tsha2 was common to astrocytes, as well.

Amino Acid Sequence↗

PubMed1998

Voltage-gated potassium channels of Schwann cells from trout lateral line nerve: a combined electrophysiological and molecular characterization.

Voltage-gated ionic currents were recorded from explant cultured and freshly dissociated SC from trout lateral line nerve using the whole-cell configuration of the patch clamp technique. In the majority of cases a delayed rectifier potassium outward current (KD) was found exclusively, which activated at potentials > or = -40 mV and reached maximal amplitudes of 240+/-25.2 nA at 60 mV testpulse potential. This current showed no voltage-dependent kinetics of inactivation and was insensitive to TEA but was effectively blocked by 4-AP. By single cell RT-PCR the transcript of a shaker-related potassium channel gene, termed tshal (a fish homologue of Kv1.2), was selectively amplified. In its biophysical and pharmacological properties the native whole cell potassium outward current of trout Schwann cells closely matched those of the cloned tshal subunit previously expressed in xenopus oocytes. A small subpopulation of freshly dissociated SC (less than 10%) at hyperpolarizing potentials elicited a potassium inward current instead, which in its kinetics closely resembled the inward rectifier (KIR) of mammalian SC. Neither voltage-gated sodium currents nor membrane currents activated by excitatory amino acids (glutamate, kainate, and quisqualate) were observed.

Animals↗

PubMed1997

Partial characterization of the 5'-flanking region of trout IP: a Po-like gene containing a PLP-like promoter.

The IP gene of trout encodes two Po-like glycoproteins which are expressed by oligodendrocytes in the fish CNS. A 679 bp fragment of its 5'-flanking region was isolated from a genomic library and sequenced. The transcription start point was determined 124 bp upstream the ATG initiator codon by primer extension analysis. Apart from a modified TATA-box and an inverted CCAAT-box located at canonical distances from the transcription start site several eucaryotic cis-acting regulatory elements were identified in the 679 bp upstream region, including an AP-1 binding site, a brain specific Sp1 motif, a cyclic AMP responsive element and a consensus sequence for POU homeodomain protein binding. The occurence of respective DNA-binding proteins for Sp1, AP-1 and POU in the nuclei of trout oligodendrocyte progenitor cells was verified by gel retardation experiments. Functional activity of various subfragments of the 679 bp upstream region was demonstrated by CAT reporter gene analysis. A computer-assisted sequence alignment of the trout IP 5'-flanking end with the corresponding region of the mammalian PLP gene promoter revealed four sites of high homology, while similarity with the mammalian Po gene promotor was low. The results are discussed with respect to the phylogenetic shift from Po-like proteins to PLP during evolution of the vertebrate CNS myelin sheath.

Animals↗

PubMed1995

Glutamate-activated ionic currents in cultured astrocytes from trout: evidence for the occurrence of non-N-methyl-D-aspartate receptors.

Glutamate-induced currents were recorded from cultured trout astrocytes with the whole-cell variation of the patch-clamp technique. Ninety percent of the tested cells were directly depolarized by the amino acid neurotransmitter in a concentration-dependent manner. The depolarizing effect was due to an inward current that reversed near 0 mV and was accompanied by a noise increase, indicating the opening of an ion channel. Ion substitution experiments revealed that the glutamate-induced current was mainly carried by sodium ions but not chloride or calcium ions. The glutamate-induced response could be mimicked by the neuronal glutamate receptor subtype agonists kainate and quisqualate, while N-methyl-D-aspartate was without detectable effect.

Animals↗

PubMed1995

Changes in ion channel expression during in vitro differentiation of trout oligodendrocyte precursor cells.

Voltage-gated ionic currents were studied in cultured trout oligodendrocyte precursor cells derived from larval trout brain with the whole-cell mode of the patch-clamp technique. These bipolar cells which carry the ganglioside epitope A2B5 on their surface differentiated in vitro into immature multipolar oligodendrocytes expressing the myelin glycoprotein IP2, which signifies the initial step of oligodendroglial development in fish CNS. Depolarization above -40 mV activated a fast transient sodium inward current that was eliminated by substituting Na+ for choline and blocked in the presence of 1 microM TTX. The kinetics and the voltage-dependence of inactivation (half-maximal inactivation at -68 mV) resembled those of sodium currents described in mammalian oligodendrocyte precursor cells and CNS neurons. The expression of Na+ channels was developmentally regulated, since high amplitudes were measured only in A2B5+ cells with a characteristic bipolar morphology of glial progenitors. Depolarizing voltage steps, additionally elicited outward potassium currents that were sensitive to external 4-AP. In a subpopulation of cells this outward current consisted of a sustained and a transient component. The amplitude of both components were dependent on the prepulse potential.

Animals↗

PubMed1995

Molecular cloning and tissue expression of a cDNA encoding IP1--a P0-like glycoprotein of trout CNS myelin.

A full-length cDNA encoding a major structural glycoprotein of trout CNS myelin (IP1) was cloned and sequenced. The deduced amino acid sequence exhibited a significant structural homology with the P0 proteins of rat PNS and shark CNS. Sequence conservation was strongest in the extracellular domain, and it included the position of the two cysteine residues required for stabilization of an immunoglobulin-like secondary structure as well as those of the single N-glycosylation acceptor site. The cytoplasmic domain was shorter by 38 amino acids than those of rat and shark P0 and except for a high proportion of basic amino acids did not show any appreciable sequence homology. A single mRNA species of 2 kb was identified by northern blotting, which was expressed in brain tissue but not in liver. By in situ hybridization a selective labeling of myelinating glial cells in the trout CNS and PNS was revealed. The developmental appearance of the IP1 transcript closely coincided with a period of active myelin deposition in most regions of the trout brain.

Amino Acid Sequence↗

PubMed1994

Voltage-dependent sodium and potassium currents in cultured trout astrocytes.

Voltage-gated ionic currents were recorded from cultured trout astrocytes with the whole-cell variation of the patch-clamp technique. In a subpopulation of astrocytes depolarizations above -40 mV activated a fast transient inward current that was identified as a sodium current by ion substitution experiments, its current reversal potential, and its TTX-sensitivity. Regarding threshold of activation, peak current voltage, and amplitude this current closely resembled those previously described for mammalian astrocytes. Voltage-dependence of inactivation and kinetics, however, markedly differed from the "glial-like" sodium current occurring in mammalian hippocampal or optic nerve astrocytes, since the sodium current of trout astrocytes exhibited a faster time course of activation and decay and a more depolarized steady-state inactivation curve with midpoints close to -60 mV. During a period of 2 weeks in culture the biophysical properties of the sodium current did not change significantly, albeit a continuous decrease in current density was observed. At depolarizing voltage steps positive to -40 mV, additionally voltage-gated potassium outward currents were evoked, which could be separated into a steady-state current with delayed rectifier properties and an inactivating component resembling the A-type current. Moreover, in a subpopulation of astrocytes an inward potassium current was elicited at hyperpolarizing potentials, which exhibited biophysical features consistent with the potassium inward rectifier of mammalian astrocytes.

Animals↗

PubMed1994

Similarities and differences between fish oligodendrocytes and Schwann cells in vitro.

In light of the striking differences between oligodendrocytes of the optic nerve/tract of adult goldfish and their mammalian counterparts, a further characterization of goldfish oligodendrocytes was performed. A comparison with Schwann cells was included because fish optic nerve/tract-derived oligodendrocytes bear remarkable similarities to this type of glial cell. Fish optic nerve/tract-derived oligodendrocytes that had differentiated into 04 and 6D2-positive cells and thus expressed early myelin marker molecules were found to incorporate BrdU and to divide in vitro over a period of weeks. For the induction of more advanced markers of myelinogenesis such as the CNS-specific myelin protein 36K, oligodendrocytes required extensive contact with axons. Other agents, such as fetal calf or carp serum, substrate components, or forscolin failed, however, to induce 36K expression. 04/6D2-positive oligodendrocytes could be distinguished from fish 6D2-positive Schwann cells derived from cranial nerves by their antigenic phenotype: Schwann cells but not oligodendrocytes exhibited the low affinity NGF receptor. While both cell types carry the cell adhesion molecules NCAM, E 587 antigen, and the L2/HNK-1 epitope, only Schwann cells possess a further adhesion molecule, Neurolin.

Animals↗

PubMed1992

Comparative analysis of sodium-dependent L-glutamate transport of synaptosomal and astroglial membrane vesicles from mouse cortex.

Uptake of [3H]L-glutamate into membrane vesicles prepared from either mouse cortical astrocyte cultures or synaptosomes was found to be an electrogenic sodium- and potassium-dependent transport process with saturable uptake kinetics. Pharmacological differences were revealed by using a variety of substrate analogues. L-trans-PDC inhibited the synaptosomal glutamate transport 2-4-fold stronger than the astroglial uptake. The substrate analogues DL-threo-beta-hydroxy-aspartate, DL-aspartate-beta-hydroxamate, L-aspartate and D-aspartate inhibited glutamate transport of astroglial and neuronal membrane vesicles in a distinctive manner, whereas D-glutamate, quisqualate and dihydrokainate had no effect in either case. Immunoblotting and immunocytochemical labeling with antibodies against the rat brain glutamate transporter revealed the selective reaction of a band at about 75 kDa mol. wt. and a specific pattern of astrocyte immunostaining.

Amino Acid Transport System X-AG↗

PubMed1992

In vitro differentiation of trout oligodendrocytes: evidence for an A2B5-positive origin.

The molecular differentiation of oligodendrocytes derived from larval trout brain was studied in dissociated cell cultures using a range of cell type and stage specific antibodies. By double-labeling immunostaining using A2B5 antibodies in conjunction with antibodies against the myelin glycoproteins IP1 and IP2 evidence was obtained that oligodendrocytes of trout in vitro originate from A2B5+ precursor cells, which in terms of morphology closely resemble 0-2A progenitors of the mammalian CNS. Most surprisingly these cells did not differentiate in vitro beyond the level of IP2 expression, which signifies the initial step of oligodendroglial development in vivo. Hence it appears that in trout oligodendrocytes the initiation of the developmental program is intrinsically regulated, whereas further maturation of the cells requires appropriate environmental stimulation.

Animals↗

PubMed1992

Neuronal and glial gamma-aminobutyric acid+ transporters are distinct proteins.

In the central nervous system, two subtypes of sodium- and chloride-coupled GABA transporter exist. One is sensitive to ACHC, the other to beta-alanine. They are thought to be of neuronal and glial origin, respectively. GABA transport in membrane vesicles derived from astroglial cells was found to be sodium- and chloride-dependent, electrogenic and much more sensitive to beta-alanine than to ACHC. Immunoblotting with antibodies directed against a variety of sequences of the ACHC-sensitive transporter indicated that none of these epitopes was shared by the glial transporter.

Amino Acids↗

PubMed1992

Characteristics of fish glial cells in culture: possible implications as to their lineage.

Regeneration of injured central nervous system axons is largely dependent on the response of the associated nonneuronal glial cells to injury. Glial cells of the mammalian central nervous system, unlike those of fish, are apparently not conducive to axonal regeneration. While the lineage of rat glial cells is well characterized and its role in the support or inhibition of regenerative growth is beginning to be understood, little is known about fish glial cells. Accordingly, glial cells in cultures of adult goldfish brain and of newly hatched goldfish larvae were studied in an attempt to establish their lineage. The cells were identified by means of indirect immunofluorescence, using antibodies against fish astrocytes and oligodendrocytes. The cell count in the cultures increased from a small number of cells at 24 h after plating to a large number of both astrocytes and oligodendrocytes after 1 week in culture. Both of these cell types had originated from proliferating cells, as shown by their uptake of tritiated thymidine and by the inhibition of cell proliferation by 5-fluoro-2'-deoxyuridine. Both astrocytes, i.e., glial fibrillary acidic protein-positive cells, and oligodendrocytes, i.e., 6D2-positive cells, were positively labeled also by A2B5 antibodies, which are known to label progenitors of type-2 astrocytes and oligodendrocytes in the rat optic nerve. The results suggest that A2B5 positive progenitor cells in the goldfish central nervous system, as in the rat optic nerve, might be a common progenitor of astrocytes and oligodendrocytes.

Animals↗