Registro:
| Documento: | Tesis Doctoral |
| Disciplina: | biologia |
| Título: | Caracterización electrofisiológica y farmacológica de los canales de calcio voltaje dependientes de los terminales motores del ratón |
| Autor: | Protti, Darío Alejandro |
| Editor: | Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales |
| Filiación: | Facultad de Medicina. Instituto de Biología Celular y Neurociencias "Prof. Dr. Eduardo de Robertis". Laboratorio de Electrofisiología
|
| Publicación en la Web: | 2017-03-01 |
| Fecha de defensa: | 1995 |
| Fecha en portada: | 1995 |
| Grado Obtenido: | Doctorado |
| Título Obtenido: | Doctor en Ciencias Biológicas |
| Director: | Uchitel, Osvaldo Daniel |
| Idioma: | Español |
| Formato: | PDF |
| Handle: |
http://hdl.handle.net/20.500.12110/tesis_n2699_Protti |
| PDF: | https://bibliotecadigital.exactas.uba.ar/download/tesis/tesis_n2699_Protti.pdf |
| Registro: | https://bibliotecadigital.exactas.uba.ar/collection/tesis/document/tesis_n2699_Protti |
| Ubicación: | Dep.BIO 002699 |
| Derechos de Acceso: | Esta obra puede ser leída, grabada y utilizada con fines de estudio, investigación y docencia. Es necesario el reconocimiento de autoría mediante la cita correspondiente. Protti, Darío Alejandro. (1995). Caracterización electrofisiológica y farmacológica de los canales de calcio voltaje dependientes de los terminales motores del ratón. (Tesis Doctoral. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales.). Recuperado de http://hdl.handle.net/20.500.12110/tesis_n2699_Protti |
Abstract:
Calcium has been identified in a wide variety of biological systems as a secondmessenger. It has been demonstrated that it has a key role in different processes such asexcitation-contraction coupling, neurotransmitter and hormone release, gene activation,some mechanisms associated with learning and memory and many other physiologicalprocesses. According to the vesicular hypothesis, Ca²+ entry into the presynaptic nerve terminalsis a pre-requisite for transmitter release. It has been shown that Ca²+ fluxes are activated bydepolarization and that the amount of transmitter release is dependent on the level ofintracellular calcium concentration. This increase in Cap concentration is achieved by theopening of voltage dependent calcium channels (VDCC) after the arrival of the actionpotential to the nerve terminal. The neuromuscular junction and the squid giant synapse have proved to be excellentpreparations to study the sequence of events that take place during synaptic transmission andare a model for understanding the synaptic mechanisms involved in chemical synapsesthroughout the animal kingdom. Different types of calcium channels have been described, according to their biophysicaland pharmacological properties. Llinas y Yarom (l981) demonstrated the coexistence of atleast two different types of calcium channels, being one of them of low threshold, LVA lowvoltage activated- and the other of high threshold HVA - high voltage activated. Later,the presence of these different calcium currents were shown in chicken DRG (dorsal rootganglion) neurones. LVA currents are activated by weak depolarizations from negativepotentials and decay rapidly after their activation. HVA currents are activated from morepositive holding potentials, and inactivate slowly. The LVA channels are known as T-type calcium channels due to their transientactivation. The HVA channels include a great number of subtypes. At least four different types of HVA channels have been distinguished at nerve cells. The L-type calcium channel issensitive to a family of organic compounds, the dihydropyridines (DHP). There are different DHP, some of them are agonists and others antagonists of the calcium channels. The N-typecalcium channels were first described as sensitive to a toxin derived from a marine snail,omega-conotoxin GVIA (ω-CgTx GVIA). There are many other polipeptides obtained fromsnail and spider venoms which block N-type calcium channels, however, ω-CgTx GVIA isthe most wider used. The P-type calcium channel, was initially described in cerebellar Purkinje cells, it was found to be insensitive to DHP and ω-CgTx GVIA, but was potentlyblocked by a low molecular weight fraction (FTX) and a polypeptide (ω-Aga-IVA), bothtoxins purified from the venom of the funnel-web spider Agelenopsis aparta. More recentlythe Q-type calcium channel was described in cerebellar granule cells. This new type ofchannel is insensitive to DHP and ω-CgTx GVIA, but sensitive to high concentrations of ω-Aga-IVA (hundreds of nanomolar), and also blocked by a polypeptide purified from the snailvenom, ω-CgTx M-VIIC. All these different channels, may coexist at a neuronal soma and also at the nerveterminals. However, in some preparations the combined use of all the calcium channelblockers, cannot suppress Ca²+ currents completely, indicating the existence of stillunidentified VDCC. Increasing information about VDCC is coming from the field of molecular biology. Molecular cloning of genes which code for the al subunit of VDCC, provided informationabout the structure of this transmembrane proteins, and the expression of its products in Xenopus oocytes made their biophysical and pharmacological characterization possible. Although it is possible to establish a relationship between the product of the genes andcalcium channels characterized ‘in situ', in many cases there is no good correlation betweenthe properties of the expressed calcium channels and those studied in situ. The existence of different VDCC, made it interesting to explore about their specificfunction and whether a particular type was responsible for synaptic transmission. Electrophysiological recording is the most confident technique to study the channelswhich take part in synaptic transmission. In 1984, Kerr and Yoshikami showed that frogneuromuscular transmission was abolished by ω-CgTx GVIA, which acted by blocking Ca²+entry into the presynaptic terminal. In contrast, ω-CgTx GVIA does not produce any effectin mammalian synaptic transmission electrically evoked in normal conditions. In the central nervous system (CNS), depending on the structure, it was shown thatdifferent VDCC subtypes are involved. At the neurosecretory terminals of theneurohypophysis it seems that both L- and N- type VDCC mediate neurosecretion (Lemosand Nowicky, 1989). Takahashi and Momiyama (1993) showed that in three different areasof the CNS, P-like and N-type VDCC are involved to varying degrees in synaptictransmission, while L-type seems not to be related with transmitter release. In the synapsebetween hipocampal CA3 and CAI neurons, transmitter release is mediated by N-typecalcium channels and other type of channels, whose pharmacology resembles Q-type calciumchannels. Stanley (1991) determined that transmitter release at the calyx synapse of chickencilliary ganglion is due to Ca²+ flux through N-type calcium channels It is also possible to have an approach about the VDCC involved in transmitterrelease, by means of colorimetric and biochemical techniques. Yawoo et al. showed that Ca²+ concentration was diminished in the presence of ω-CgTx GVIA, from what derives that N-type calcium channels mediate calcium entry at the chick cilliary ganglion synapse. Manygroups showed that K+ evoked neurotransmitter release in CNS slices, is inhibited by coCng GVIA as well as by ω-Aga-IVA, depending on the neurotransmitter and the areastudied (Turner et al., 1992; Kimura et al., 1994). At the mammalian neuromuscular junction, under normal conditions, transmitterrelease is resistant to DHP and to ω-CgTx GVIA, indicating that neither L nor N-type VDCC are mediating transmitter release. However, in cut muscle fibres it was reported that L-type channels antagonists diminish quantal content, when release is previously stimulatedby the L-type channel agonist BayK 8644 (Atchinson, 1987). It was also reported that ω-CgTx GVIA prevents the facilitatory effects of noradrenaline on the evoked release of [³H] Acetylcholine from mammalian motor nerve terminals (Wessler et al., 1990).
Citación:
---------- APA ----------
Protti, Darío Alejandro. (1995). Caracterización electrofisiológica y farmacológica de los canales de calcio voltaje dependientes de los terminales motores del ratón. (Tesis Doctoral. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales.). Recuperado de https://hdl.handle.net/20.500.12110/tesis_n2699_Protti
---------- CHICAGO ----------
Protti, Darío Alejandro. "Caracterización electrofisiológica y farmacológica de los canales de calcio voltaje dependientes de los terminales motores del ratón". Tesis Doctoral, Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales, 1995.https://hdl.handle.net/20.500.12110/tesis_n2699_Protti
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