Biomedical subjects

Philippe Lory

Publications and source records attributed to Philippe Lory.

24 records · Page 2Linked to original sources

PubMed2004

Lymphocyte calcium signaling involves dihydropyridine-sensitive L-type calcium channels: facts and controversies.

Calcium influx into lymphocytes is essential for activation, differentiation, and effector functions. While several channel- and receptor-types contribute to calcium influx, voltage-gated calcium channels (VGCC) mediate a well-characterized calcium influx pathway that is most exclusively identified in excitable cells. The role of L-type VGCCs, which belong to high-voltage activated calcium channels and are defined as dihydropyridine (DHP) receptors in excitable cells, is well documented. Interestingly, while lymphocytes do not range in the excitable cell category, the modulatory role of DHP agonists and antagonists and the identification of L-type VGCC-related molecules in B and T lymphocytes, mainly in Th2 cells, suggest these proteins are involved in the calcium response of these cells. Because the identity and the regulation of DHP receptors/channels in lymphocytes is far from being solved, we will discuss the challenging issues of demonstrating a role of L-type VGCCs in nonexcitable cells and the arguments supporting their role in lymphocytes. We will comment on the limitation of the use of DHP agonists and antagonists to ascertain a specific involvement of L-type VGCCs in lymphocyte calcium signaling. Finally, we will provide new clues on the interest of a potential use of DHP antagonists in Th2-cell-mediated pathology.

Calcium Channels, L-Type↗

PubMed2003

[Functional specificity of T-type calcium channels and their roles in neuronal differentiation].

Calcium plays a central role in cell signaling and T-type calcium channels constitute a unique route for the entry of calcium ions in excitable cells. The genuine electrophysiological properties of T-type calcium channels include activation at low voltages and window currents in the range of cell membrane resting potential. T-type channels therefore generate a specific calcium influx likely to play an important role during early stages of development, in various cellular functions including cell proliferation, cell differentiation, gene transcription and hormone secretion. Such T-channel activities are also associated with several pathological situations. With the recent cloning of three T-type pore channel subunits, alpha 1G, alpha 1H and alpha 1I (also called Cav3.1, Cav3.2 and Cav3.3, respectively), it has become possible to investigate further the role of T-type channels in various cellular functions, including neuronal differentiation. Here we describe recent data obtained in our laboratory demonstrating how T-type channels generated by the alpha 1H subunit contribute to neuronal differentiation.

Animals↗

PubMed2002

Neuronal T-type alpha 1H calcium channels induce neuritogenesis and expression of high-voltage-activated calcium channels in the NG108-15 cell line.

Neuronal differentiation involves both morphological and electrophysiological changes, which depend on calcium influx. Voltage-gated calcium channels (VGCCs) represent a major route for calcium entry into neurons. The recently cloned low-voltage-activated T-type calcium channels (T-channels) are the first class of VGCCs functionally expressed in most developing neurons, as well as in neuroblastoma cell lines, but their roles in neuronal development are yet unknown. Here, we document the part played by T-channels in neuronal differentiation. Using NG108-15, a cell line that recapitulates early steps of neuronal differentiation, we demonstrate that blocking T-currents by nickel, mibefradil, or the endogenous cannabinoid anandamide prevents neuritogenesis without affecting neurite outgrowth. Similar results were obtained using antisense oligodeoxynucleotides directed against the alpha1H T-channel subunit. Furthermore, we describe that inhibition of alpha1H T-channel activity impairs concomitantly, but independently, both high-voltage-activated calcium channel expression and neuritogenesis, providing strong evidence for a dual role of T-channels in both morphological and electrical changes at early stages of neuronal differentiation.

Animals↗

PubMed2002

Specific contribution of human T-type calcium channel isotypes (alpha(1G), alpha(1H) and alpha(1I)) to neuronal excitability.

In several types of neurons, firing is an intrinsic property produced by specific classes of ion channels. Low-voltage-activated T-type calcium channels (T-channels), which activate with small membrane depolarizations, can generate burst firing and pacemaker activity. Here we have investigated the specific contribution to neuronal excitability of cloned human T-channel subunits. Using HEK-293 cells transiently transfected with the human alpha(1G) (Ca(V)3.1), alpha(1H) (Ca(V)3.2) and alpha(1I) (Ca(V)3.3) subunits, we describe significant differences among these isotypes in their biophysical properties, which are highlighted in action potential clamp studies. Firing activities occurring in cerebellar Purkinje neurons and in thalamocortical relay neurons used as voltage clamp waveforms revealed that alpha(1G) channels and, to a lesser extent, alpha(1H) channels produced large and transient currents, while currents related to alpha(1I) channels exhibited facilitation and produced a sustained calcium entry associated with the depolarizing after-potential interval. Using simulations of reticular and relay thalamic neuron activities, we show that alpha(1I) currents contributed to sustained electrical activities, while alpha(1G) and alpha(1H) currents generated short burst firing. Modelling experiments with the NEURON model further revealed that the alpha(1G) channel and alpha(1I) channel parameters best accounted for T-channel activities described in thalamocortical relay neurons and in reticular neurons, respectively. Altogether, the data provide evidence for a role of alpha(1I) channel in pacemaker activity and further demonstrate that each T-channel pore-forming subunit displays specific gating properties that account for its unique contribution to neuronal firing.

Action Potentials↗

PubMed2002

Alpha(1H) mRNA in single skeletal muscle fibres accounts for T-type calcium current transient expression during fetal development in mice.

Calcium channels are essential for excitation-contraction coupling and muscle development. At the end of fetal life, two types of Ca(2+) currents can be recorded in muscle cells. Whereas L-type Ca(2+) channels have been extensively studied, T-type channels have been poorly characterized in skeletal muscle. We describe here the functional and molecular properties of T-type calcium channels in developing mouse skeletal muscle. The T-type current density increased transiently during prenatal myogenesis with a maximum at embryonic day E16 followed by a drastic decrease until birth. This current showed similar electrophysiological and pharmacological properties at all examined stages. It displayed a wide window current centred at about -35 and -55 mV in 10 and 2 mM external Ca(2+), respectively. Activation and inactivation kinetics were fast (3 and 16 ms, respectively). The current was inhibited by nickel and amiloride with an IC(50) of 5.4 and 156 microM, respectively, values similar to those described for cloned T-type alpha(1H) channels. Whole muscle tissue RT-PCR analysis revealed mRNAs corresponding to alpha(1H) and alpha(1G) subunits in the fetus but not in the adult. However, single-fibre RT-PCR demonstrated that only alpha(1H) mRNA was present in prenatal fibres, suggesting that the alpha(1G) transcript present in muscle tissue must be expressed by non-skeletal muscle cells. Altogether, these results demonstrate that the alpha(1H) subunit generates functional T-type calcium channels in developing skeletal muscle fibres and suggest that these channels are involved in the early stages of muscle differentiation.

Animals↗

PubMed2002

Characterization and functional expression of cDNAs encoding thyrotropin-releasing hormone receptor from Xenopus laevis.

Thyrotropin-releasing hormone receptor (TRHR) has already been cloned in mammals wherethyrotropin-releasing hormone (TRH) is known to act as a powerful stimulator of thyroid-stimulating hormone (TSH) secretion. The TRH receptor of amphibians has not yet been characterized, although TRH is specifically important in the adaptation of skin color to environmental changes via the secretion of alpha-melanocyte-stimulating hormone (alpha-MSH). Using a dege-nerate PCR strategy, we report on the isolation of three distinct cDNA species encoding TRHR from the brain of Xenopus laevis. We have designated these as xTRHR1, xTRHR2 and xTRHR3. Analysis of the predicted amino acid sequences revealed that the three Xenopus TRHRs are only 54-62% identical and contain all the highly conserved residues constituting the TRH binding pocket. Amino acid sequences and phylogenetic analysis revealed that xTRHR1 is a member of TRHR subfamily 1 and xTRHR2 belongs to subfamily 2, while xTRHR3 is a new TRHR subtype awaiting discovery in other animal species. The three Xeno-pus TRHRs have distinct patterns of expression. xTRHR3 was abundant in the brain and much scarcer in the peripheral tissues, whereas xTRHR1 was found mainly in the stomach and xTRHR2 in the heart. The Xenopus TRHR subtype 1 was found specifically in the intestine, lung and urinary bladder. These observations suggest that the three xTRHRs each have specific functions that remain to be elucidated. Expression in Xenopus oocytes and HEK-293 cells indicates that the three Xenopus TRHRs are fully functional and are coupled to the inositol phosphate/calcium pathway. Interestingly, activation of xTRHR3 required larger concentrations of TRH compared with the other two receptors, suggesting marked differences in receptor binding, coupling or regulation.

Amino Acid Sequence↗