Biomedical subjects
M Biel
Publications and source records attributed to M Biel.
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.
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.
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.
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.
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.
Tissue-specific expression of high-voltage-activated dihydropyridine-sensitive L-type calcium channels.
The cloning of the cDNA for the alpha 1 subunit of L-type calcium channels revealed that at least two genes (CaCh1 and CaCh2) exist which give rise to several splice variants. The expression of mRNA for these alpha 1 subunits and the skeletal muscle alpha 2/delta, beta and gamma subunits was studied in rabbit tissues and BC3H1 cells. Nucleic-acid-hybridization studies showed that the mRNA of all subunits are expressed in skeletal muscle, brain, heart and aorta. However, the alpha 1-, beta- and gamma-specific transcripts had different sizes in these tissues. Smooth muscle and heart contain different splice variants of the CaCh2 gene. The alpha 1, beta and gamma mRNA are expressed together in differentiated but not in proliferating BC3H1 cells. A probe specific for the skeletal muscle alpha 2/delta subunit did not hybridize to poly(A)-rich RNA from BC3H1 cells. These results suggest that different splice variants of the genes for the alpha 1, beta and gamma subunits exist in tissues containing L-type calcium channels, and that their expression is regulated in a coordinate manner.
High voltage activated calcium channels: molecular composition and function.
Voltage-activated calcium channels comprise a group of similar yet distinct proteins or protein complexes that differ in electrophysiological properties, modulation by phosphorylation and GTP-binding proteins and in their relative sensitivity to organic calcium channel blockers. Cloning of the cDNA of L-type calcium channels from skeletal muscle, heart and smooth muscle opens the way to understanding the molecular basis of channel function and regulation and provides means of studying calcium channels in other tissues.
Primary structure and functional expression of a high voltage activated calcium channel from rabbit lung.
The complete amino acid sequence of the receptor for organic calcium channel blockers (CaCB) from rabbit lung has been deduced by cloning and sequence analysis of the cDNA. Synthetic RNA derived from this cDNA induces the formation of a functional CaCB-sensitive high voltage activated calcium channel in Xenopus oocytes.
The cDNA and deduced amino acid sequence of the gamma subunit of the L-type calcium channel from rabbit skeletal muscle.
Complementary DNAs for the gamma subunit of the calcium channel of rabbit skeletal muscle were isolated on the basis of peptide sequences derived from the purified protein. The deduced primary structure is without homology to other known protein sequences and is consistent with the gamma subunit being an integral membrane protein.
Primary structure of the beta subunit of the DHP-sensitive calcium channel from skeletal muscle.
Complementary DNAs for the beta subunit of the dihydropyridine-sensitive calcium channel of rabbit skeletal muscle were isolated on the basis of peptide sequences derived from the purified protein. The deduced primary structure is without homology to other known protein sequences and is consistent with the beta subunit being a peripheral membrane protein associated with the cytoplasmic aspect of the sarcolemma. The protein contains sites that might be expected to be preferentially phosphorylated by protein kinase C and guanosine 3',5'-monophosphate-dependent protein kinase. A messenger RNA for this protein appears to be expressed in brain.
Neurologists' knowledge of medication costs.
Using mailed questionnaires, neurologists were asked for (1) estimates of retail prices for 39 common drugs, (2) attitudes about drug costs, and (3) implications for clinical practice. Among these practitioners, (1) more product prices were overestimated than underestimated, (2) old products were as unfamiliar as new products, and (3) community practitioners were more aware of prices than academic neurologists and trainees, but still made errors. Future studies should also consider physician prescribing behavior in terms of adherence to recommended laboratory tests and patient inconvenience factors. Neurologists should be aware of alternative prescription outlets for patients.
Submersion accidents and epilepsy.
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Maintenance of fetal hemoglobin (HbF) elevations in the baboon by prolonged erythropoietic stress.
We have previously shown that acute erythropoietic (Ep) stress by hemolysis or hypobaric hypoxia causes elevations of HbF in the baboon. The magnitude of these elevations is genetically determined, ranging from 3% to 60% (low, intermediate, and high responders). These genetic differences in HbF levels among animals are mainly due to differences in the number of HbF-containing cells ("F-cells"). The present study was undertaken to study the influence of prolongation and of the severity of Ep stress on HbF levels and the number of F-cells. The packed cell volume (PCV) of the blood of 4 animals, approximately 3 yr old, was maintained at 20% by daily phlebotomies, and the animals were exposed to varying degrees of hypobaric hypoxia for up to 40 days. In these experiments, the number of F-cells increased rapidly and reached individually constant levels ranging from 60% to 80%, when the PCV reached 20%, and no further increase was observed regardless of the subsequent degree of hypoxia. On the other hand, HbF levels, and with it the values for HbF per F-cell, increased proportionally to the severity of the Ep stress and could be maintained at a constant level dependent on the degree of the hypoxia, e.g., at 19,000 feet HbF levels of one animal remained 20%-25% throughout the duration of the exposure of 14 days. These data are indicative of separate control of F-cell numbers and of the levels of HbF per F-cell. It appears that with the increase of Ep stress, those Ep stem cells that have retained the HbF program are mobilized into maturation. A model, attempting to explain this phenomenon is presented.
Epileptics and school personnel.
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Genetic relationship between fetal Hb levels in normal and erythropoietically stressed baboons.
Previous studies have shown that the magnitude of the fetal haemoglobin (Hb F) response to haemolytic anaemia and hypobaric hypoxia in the baboon is specific to an animal ('high and low Hb F responders'), suggesting that the Hb F response is under genetic control. In this study Hb F levels in 55 adult (over 8 years old) and 23 juvenile unstressed baboons varied between 0.02% and 0.6% ('resting Hb F levels'). Twenty-nine of these animals were subjected to haemolytic stress and the magnitude of their Hb F response was positively correlated with the resting Hb F levels. In addition, the resting levels of Hb F in parents were positively correlated with those of their offspring. In 11 animals, seven adults and four juveniles, subjected to haemopoietic stress the Hb F levels were increased proportionally to the number of F-cells. In juvenile animals the calculated concentration of Hb F per F-cell was markedly higher than in adult animals. These data demonstrate that the resting level of Hb F is predictive of the magnitude of the Hb F response to stress erythropoiesis. The number of F-cells and the concentration of Hb F per cell in erythropoietic stress appear to be modulated by different mechanisms.
Comparative study of the native fluorescence of human dentine and bovine skin collagens.
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[Multiple Ewing sarcoma in a dog].
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