ABSTRACT
En este trabajo se estudió la participación que tiene la liberación de calcio del retículo endoplásmico en la liberación de serotonina en terminales sinápticas. Los experimentos se llevaron a cabo en sinapsis formadas en cultivo entre neuronas serotonérgicas de Retzius y neuronas mecanosensoriales sensibles a presión, aisladas del Sistema Nervioso Central de la sanguijuela. En esta preparación la estimulación con pares de impulsos produjo facilitación sináptica. La estabilización de los receptores de rianodina en un estado de sub-conductancia por la incubación con rianodina 100 μM produjo un alargamiento del potencial sináptico en respuesta a impulsos presinápticos, sugiriendo que el calcio liberado por estos canales puede alcanzar las vesículas y promover la secreción. En contraste, el vaciamiento de los depósitos intracelulares de calcio con tapsigargina 500 nM produjo una disminución gradual de la facilitación sináptica ante impulsos presinápticos pareados y abolió la liberación extrasináptica en el axón neuronal en respuesta a trenes de impulsos. Todo esto ocurrió sin cambios en las propiedades de la membrana postsináptica, lo cual sugiere que la liberación de calcio intracelular participa en un mecanismo de retroalimentación positiva que promueve la liberación presináptica y perisináptica en las neuronas serotonérgicas.
This work analyses the role of intracellular calcium pools in serotonin release from nerve terminals. Experiments were carried out in synapses formed in culture between serotonergic Retzius neurones and pressure mechanosensory neurons, isolated from the Central Nervous System of the leech. In this configuration, serotonin is released from clear vesicles at synapses or from extrasynaptic dense core vesicles. Locking ryanodine receptors in a subconductance state by incubation with 100 μM ryanodine caused an elongation of the synaptic potential in response to a presynaptic action potential or to trains of them, suggesting that calcium released from the endoplasmic reticulum through these channels reaches the synaptic vesicles and may promote their fusion with the plasma membrane. By contrast, depletion of intracellular calcium pools by incubation with 500 nM thapsigargin gradually decreased paired-pulse synaptic facilitation and abolished extrasynaptic axonal serotonin release in response to trains of impulses. All this occurred without changes in the properties of the postsynaptic membrane, indicating that intracellular calcium release participates in a feedback mechanism that enhances presynaptic and perisynaptic release in serotonergic neurons.
ABSTRACT
Ca2+ sparks represent synchronous opening of the ryanodine receptor (RyR) Ca2+ release channels located at the sarcoplasmic reticulum (SR) membrane. Whereas a quantal nature of Ca2+ sparks has been defined in cardiac muscle, the regulation of Ca2+ sparks in skeletal muscle has not been well-studied. Osmotic-stress applied to an intact skeletal muscle fiber can produce brief Ca2+ sparks and prolonged Ca2+ burst events. Here, we show that termination of Ca2+ bursts occurs in a step wise and quantal manner. Ca2+ burst events display kinetic features that are consistent with the involvement of both stochastic attrition and coordinated closure of RyR channels in the termination of SR Ca2+ release. Elemental unitary transition steps could be defined with a mean DF/F0 of ~0.28, corresponding to the gating of 1-2 RyR channels. Moreover, the amplitude of the elemental transition steps declines at the later stage of the burst event. In tandem Ca2+ burst events where two Ca2+ bursts occur at the same position within a fiber in rapid succession, the trailing event is consistently of lower amplitude than the initial event. These two complementary results suggest that SR Ca2+ release may be associated with local depletion of SR Ca2+ stores in mammalian skeletal muscle.
Subject(s)
Animals , Calcium/metabolism , Calcium Signaling , Male , Mammals , Mice , Muscle Fibers, Skeletal/cytology , Muscle Fibers, Skeletal/metabolism , Muscle Fibers, Skeletal/metabolism , Muscle, Skeletal/cytology , Muscle, Skeletal/metabolism , Muscle, Skeletal/metabolism , Osmotic Pressure , Time FactorsABSTRACT
Objective Ryanodine receptor (RyR) is one of the Ca2+ release channels on the intracellular Ca2+ stores. RyR induced-Ca2+ release is activated by the voltage-dependent Ca2+ entry, that is, calcium-induced calcium release (CICR). Intracellular free Ca2+ concentration (ECa2+]i) plays a key role on cochlear function. Our study is to investigate the differential expression of RyR in the developing rat cochlea, and to analyze the relationship between the expression of RyR and auditory functional development. Methods Immature SD rats, which were 1 day (P1), 5 days (P5), 10 days (P10), 14 days (P14), 28 days (P28) after parturition, and adutl rats(5 rats for each age) were included in the study. Frozen cochlea sectioning and immunofluorescence were applied to observe the differential expression of RyR. Results The RyR expression in the Corti's organ increased during the cochlear development. It's not significant that the stain was observed on the hair cells and supporting cells in the Corti's organ of P1 and P5 rats. The appearance of the Corti's organ of P10 rats trended to maturity. In P14 rats the RyR expression on hair cells located in the synaptic area against the afferent or efferent nerve, and the strain on supporting cells was extensive. There was little different between the strain on cochlea of P14 and P28 rats. In postmature rat spiral ganglion neurons (SGN), the RyR expression verged gradually from extensive whole cell soma to the synaptic area near to the plasma membrane. Conclusion The RyR expression peaked the 14th day after parturition, which was close to that in the mature cochlea. The time course of the RyR expression during the cochlear development was coincident with that of the auditory functional development. The RyR expression on both hair cells and SGNs located in the synaptic area near to the plasmolemma, implying that RyR induced-CICR was related to the auditory functions such as neurotransmission. Extensive RyR expression in the soma of SGNs at the early stage possibly involved in apoptosis of SGNs during neuron development.
ABSTRACT
ABSTRACT Calcium homeostasis is of crucial importance for the function of cardial myocytes in normal electrical and mechanical processes. The sarcoplasmic reticular Ca-ATPase and the sar-colemmic Na/Ca exchanger contribute mainly to the steady state of calcium in the myoplasm. The Na/Ca exchanger serves as the principal calcium extrusion mechanism and regulates calcium content of the sarcoplasmic reticulum by regulating the resting [Ca2+]i level, through which the Na/Ca exchanger regulates the force of contraction sequentially. Very small calcium entry can trigger significant sarcoplasmic reticular calcium release (CICR). During the upstroke and plateau phasesof the action potential, There is evidence that indicates Ca2+ influx via the Na/Ca exchanger, and the depolarisation-induced calcium entry on Na/Ca exchange may contribute mainly to triggering intra-cellular calcium release. Na/Ca exchange should be reevaluated as a route through which Ca2+, as a triggering signal, enters cardiac myocyte during excitation-contraction coupling.