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M Biel

Publications and source records attributed to M Biel.

At least 37 records · Page 2Linked to original sources
PubMed1998

An isoform of the rod photoreceptor cyclic nucleotide-gated channel beta subunit expressed in olfactory neurons.

Sensory transduction in olfactory neurons involves the activation of a cyclic nucleotide-gated (CNG) channel by cAMP. Previous studies identified a CNG channel alpha subunit (CNG2) and a beta subunit (CNG5), which when heterologously expressed form a channel with properties similar but not identical to those of native olfactory neurons. We have cloned a new type of CNG channel beta subunit (CNG4. 3) from rat olfactory epithelium. CNG4.3 derives from the same gene as the rod photoreceptor beta subunit (CNG4.1) but lacks the long, glutamic acid-rich domain found in the N terminus of CNG4.1. Northern blot and in situ hybridization revealed that CNG4.3 is expressed specifically in olfactory neurons. Expression of CNG4.3 in human embryonic kidney 293 cells did not lead to detectable currents. Coexpression of CNG4.3 with CNG2 induced a current with significantly increased sensitivity for cAMP whereas cGMP affinity was not altered. Additionally, CNG4.3 weakened the outward rectification of the current in the presence of extracellular Ca2+, decreased the relative permeability for Ca2+, and enhanced the sensitivity for L-cis diltiazem. Upon coexpression of CNG2, CNG4.3, and CNG5, a conductance with a cAMP sensitivity greater than that of either the CNG2/CNG4.3 or the CNG2/CNG5 channel and near that of native olfactory channel was observed. Our data suggest that CNG4.3 forms a subunit of the native olfactory CNG channel. The expression of various CNG4 isoforms in retina and olfactory epithelium indicates that the CNG4 subunit may be necessary for normal function of both photoreceptor and olfactory CNG channels.

Amino Acid Sequence↗
PubMed1998

Three amino acids in the C-linker are major determinants of gating in cyclic nucleotide-gated channels.

The activation of cyclic nucleotide-gated (CNG) channels is a complex process comprising the initial ligand binding and a consecutive allosteric transition from a closed to an open configuration. The cone and olfactory CNG channels differ considerably in cyclic nucleotide affinity and efficacy. In each channel, the cyclic nucleotide-binding site is connected to the last transmembrane segment of the channel by a linker peptide (C-linker) of approximately 90 amino acids. Here we report that replacement of three amino acids in the cone C-linker by the corresponding amino acids of the olfactory channel (I439V, D481A and D494S) profoundly enhanced the cAMP efficacy and increased the affinities for cAMP and cGMP. Unlike the wild-type cone channel, the mutated channel exhibited similar single-channel kinetics for both cGMP and cAMP, explaining the increase in cAMP efficacy. We thus conclude that the identified amino acids are major determinants of channel gating.

Amino Acid Sequence↗
PubMed1998

Cyclic nucleotide-gated channels--mediators of NO:cGMP-regulated processes.

Cyclic nucleotide-gated (CNG) channels represent one of the three known cellular receptor classes for cGMP. Activation of CNG channels by binding of cyclic nucleotides to a site in the C-terminus results in opening of the channel pore, entry of Ca2+ into the cell and subsequent induction of Ca2+-dependent processes. In this review we will summarize new data on the complex molecular structure and the activation mechanism of CNG channels. In addition, we will discuss the role of CNG channels as mediators of NO:cGMP-dependent cellular processes.

Animals↗
PubMed1997

Molecular cloning of cyclic nucleotide-gated cation channel subunits from rat pineal gland.

We have investigated the subunit composition and the molecular structure of the CNG channel expressed in rat pineal gland. Three types of subunits have been cloned: an alpha-subunit (CNG1), two beta-subunit splice variants (rCNG4.1 and rCNG4.2) and a hydrophilic glutamic acid-rich protein (rGARP). In situ hybridization with sections of rat brain revealed the co-expression of CNG1, CNG4 and GARP in pinealocytes. In addition, CNG4-specific transcripts were detected in the arcuate, periventricular and supraoptic nuclei of the hypothalamus.

Alternative Splicing↗
PubMed1996

Molecular cloning and expression of the Modulatory subunit of the cyclic nucleotide-gated cation channel.

The cDNA of three variants of a cyclic nucleotide-gated (CNG) channel modulatory subunit (CNG4c-CNG4e) has been cloned. CNG4c, CNG4d, and CNG4e differ slightly from each other within an amino-terminal sequence that was originally reported as part of the bovine retinal glutamic acid-rich protein (GARP). The core region of CNG4 is homologous to the second subunit of the human rod photoreceptor channel (hRCNC2b), suggesting that both proteins are alternatively spliced products of the bovine and human homologue of the same gene. CNG4 transcripts are present in retina, testis, kidney, heart, and brain. Expression of CNG4 in HEK293 cells did not lead to detectable currents. Coexpression of CNG4 with the principal subunit of the bovine testis CNG channel (CNG3) resulted in currents which differed in several aspects from that induced by CNG3 alone. The heterooligomeric CNG3/CNG4 and the homooligomeric CNG3 channels were modified by Ca2+-calmodulin and some calmodulin antagonists. The results suggest that CNG4 forms functional heterooligomeric channels with CNG3 in vitro and probably also in intact tissues.

Amino Acid Sequence↗
PubMed1995

Molecular diversity of cyclic nucleotide-gated cation channels.

Cyclic nucleotide-gated cation channels (CNG channels) form a multi-gene family consisting of at least five distinct members (CNG1-5). Expression studies have indicated that only CNG1-3 are able to form functional homooligomeric channels. Although structurally related, the cDNAs of CNG4-5 fail to induce cyclic nucleotide-dependent currents when expressed alone. However, when co-expressed with CNG1-3 they confer some of the physiologically observed properties of native CNG channels which are absent from the homooligomeric CNG1-3 channels. CNG channels are expressed in several tissues and cell types pointing to a general function of these channels in a wide variety of cellular systems. There is now increasing evidence that a major function of CNG channels may consist in providing a second messenger-regulated pathway for Ca2+ influx.

Amino Acid Sequence↗
PubMed1994

Another member of the cyclic nucleotide-gated channel family, expressed in testis, kidney, and heart.

Cyclic nucleotide-gated cation channels are essential in visual and olfactory signal transduction. An additional member of the cGMP-gated channel family, termed CNG-3, has been cloned from bovine kidney. Its deduced amino acid sequence is 60% and 62% identical with the CNG-channel proteins from bovine rod outer segment and bovine olfactory epithelium, respectively. Northern analysis and sequences amplified by the PCR showed that the CNG-3 mRNA is present in testis, kidney, and heart. Calcium permeated the expressed channel in the presence of extracellular Mg2+ and Na+ at membrane potentials from -100 to +45 mV. It is likely that CNG-3 protein is responsible for cGMP-induced Ca2+ entry in cells other than sensory cells.

Animals↗
PubMed1994

Expression of cyclic nucleotide-gated cation channels in non-sensory tissues and cells.

Using a combination of PCR based cloning and Northern blot analysis we have investigated the tissue expression of cyclic nucleotide-gated (CNG) cation channels in a variety of non-excitable tissues and cells. Partial sequences of all three known CNG channels and of an auxiliary subunit of the rod photoreceptor channel were determined. The expression of CNG channel genes is both tissue and species specific. Southern blot analysis with human genomic DNA revealed specific patterns of hybridization with probes derived from the different CNG channel types indicating that they are encoded by distinct genes. Analysis of human genomic sequences showed that all three genes are derived from a common ancestral gene and might have a similar gene structure. We were not able to identify additional genes encoding CNG channels. The CNG3 channel, which was originally cloned from bovine kidney may be expressed also in bovine cone photoreceptor cells. These data suggest that some of the effects of cGMP in peripheral tissues and cells might involve the activation of CNG channels.

Animals↗
PubMed1994

Cardiac calcium channels expressed in Xenopus oocytes are modulated by dephosphorylation but not by cAMP-dependent phosphorylation.

Enhancement of cardiac L-type Ca2+ channel activity by norepinephrine via phosphorylation by protein kinase A (PKA) underlines the positive inotropic effect of this transmitter and is a classical example of an ion channel modulation. However, it is not clear whether the channel protein itself (and which subunit) is a substrate for PKA. We have expressed various combinations of the cardiac Ca2+ channel subunits in Xenopus oocytes by injecting subunit mR-NAs. Expression of beta or alpha 2/delta + beta subunits potentiated the native (endogenous) Ca2+ channel currents in the oocyte (similar to T or N but not L-type). This potentiated endogenous current was enhanced by intracellular injection of cAMP or of the catalytic subunit of PKA, and this effect was reversed by the injection of a PKA inhibitor suggesting the presence of basal phosphatase activity. When a cardiac channel of alpha 1 + beta, alpha 1 + alpha 2/delta or alpha 1 + alpha 2/delta + beta composition was expressed at levels high enough that the contribution of the endogenous current became negligible, cAMP and PKA failed to increase the Ca2+ channel current, whereas PKA inhibitors and the catalytic subunit of protein phosphatase 1 reduced the amplitude of the current. Reduction of the current by PKA inhibitors was observed regardless of the presence of the beta subunit, suggesting a major role for the alpha 1 subunit in this process. These results suggest that, like in the heart, when expressed in Xenopus oocytes, the cardiac L-type Ca2+ channels are phosphorylated in basal state and dephosphorylation reduces their activity. However, unlike the situation in the heart, the activity of the channel cannot be enhanced by PKA-catalyzed phosphorylation, suggesting that the channel is already fully phosphorylated in its basal state.

Animals↗
PubMed1993

Primary structure and functional expression of a cyclic nucleotide-gated channel from rabbit aorta.

Sequences specific for cyclic nucleotide-gated channels (CNG channels) have been amplified by PCR from cDNA of heart, aorta, sino-atrial node, cerebellum, C-cells and kidney. The complete amino acid sequence of a CNG channel from rabbit aorta has been deduced by cloning and sequence analysis of the cDNA. Synthetic RNA derived from this cDNA induces the formation of a functional CNG channel in Xenopus oocytes.

Amino Acid Sequence↗
PubMed1993

Anterior occipital cervical reconstruction with a free vascularized osteocutaneous graft: a case report.

Free vascularized osteocutaneous bone grafts are an unusual but effective method to reconstruct complex and extensive defects of skin and bone of the extremities due to trauma, tumor, or infections. Many recent publications support their utility in these situations. In distinction, little literature exists to document the use of free vascularized osteocutaneous flaps in the spine. This is likely due to the infrequent occurrence of concomitant skin and osseous defects that are not manageable by routine spinal and plastic surgical approaches. We recently managed a particularly challenging patient in whom six prior operations--three anterior and three posterior--to decompress and stabilize the occipital-cervical junction had failed. We used a free vascularized distal radius osteocutaneous flap for three purposes: to provide the patient with an optimal chance to obtain an extensive and critically important anterior occipital-cervical arthrodesis, to supply a stable soft tissue envelope for protection of a tenuous dural repair, and to reconstruct an atrophic and scarred posterior pharyngeal wall. We are unaware of any report to date that documents the use of a graft of this type in the spine. We wrote this brief article to document the indications for this operation, to illustrate the problems we encountered in this difficult reconstructive situation, and to report on the progress of our patient to date.

Adolescent↗
PubMed1992

Modulation of cardiac Ca2+ channels in Xenopus oocytes by protein kinase C.

L-Type calcium channel was expressed in Xenopus laevis oocytes injected with RNAs coding for different cardiac Ca2+ channel subunits, or with total heart RNA. The effects of activation of protein kinase C (PKC) by the phorbol ester PMA (4 beta-phorbol 12-myristate 13-acetate) were studied. Currents through channels composed of the main (alpha 1) subunit alone were initially increased and then decreased by PMA. A similar biphasic modulation was observed when the alpha 1 subunit was expressed in combination with alpha 2/delta, beta and/or gamma subunits, and when the channels were expressed following injection of total rat heart RNA. No effects on the voltage dependence of activation were observed. The effects of PMA were blocked by staurosporine, a protein kinase inhibitor. beta subunit moderate the enhancement caused by PMA. We conclude that both enhancement and inhibition of cardiac L-type Ca2+ currents by PKC are mediated via an effect on the alpha 1 subunit, while the beta subunit may play a mild modulatory role.

Alkaloids↗
PubMed1992

Calcium channel beta subunit heterogeneity: functional expression of cloned cDNA from heart, aorta and brain.

Complementary DNAs encoding three novel and distinct beta subunits (CaB2a, CaB2b and CaB3) of the high voltage activated (L-type) calcium channel have been isolated from rabbit heart. Their deduced amino acid sequence is homologous to the beta subunit originally cloned from skeletal muscle (CaB1). CaB2a and CaB2b are splicing products of a common primary transcript (CaB2). Northern analysis and specific amplification of CaB2 and CaB3 specific cDNAs by polymerase chain reactions showed that CaB2 is predominantly expressed in heart, aorta and brain, whereas CaB3 is most abundant in brain but also present in aorta, trachea, lung, heart and skeletal muscle. A partial DNA sequence complementary to a third variant of the CaB2 gene, subtype CaB2c, has also been cloned from rabbit brain. Coexpression of CaB2a, CaB2b and CaB3 with alpha 1heart enhances not only the expression in the oocyte of the channel directed by the cardiac alpha 1 subunit alone, but also effects its macroscopic characteristics such as drug sensitivity and kinetics. These results together with the known alpha 1 subunit heterogeneity, suggest that different types of calcium currents may depend on channel subunit composition.

Amino Acid Sequence↗
PubMed1991

The roles of the subunits in the function of the calcium channel.

Dihydropyridine-sensitive voltage-dependent L-type calcium channels are critical to excitation-secretion and excitation-contraction coupling. The channel molecule is a complex of the main, pore-forming subunit alpha 1 and four additional subunits: alpha 2, delta, beta, and gamma (alpha 2 and delta are encoded by a single messenger RNA). The alpha 1 subunit messenger RNA alone directs expression of functional calcium channels in Xenopus oocytes, and coexpression of the alpha 2/delta and beta subunits enhances the amplitude of the current. The alpha 2, delta, and gamma subunits also have pronounced effects on its macroscopic characteristics, such as kinetics, voltage dependence of activation and inactivation, and enhancement by a dihydropyridine agonist. In some cases, specific modulatory functions can be assigned to individual subunits, whereas in other cases the different subunits appear to act in concert to modulate the properties of the channel.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗