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Nicola Fameli

Publications and source records attributed to Nicola Fameli.

6 recordsLinked to original sources
arXiv2014

Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling

We demonstrate how nanojunctions between lysosomes and sarcoplasmic reticulum (L-SR junctions) serve to couple lysosomal activation to regenerative, ryanodine receptor-mediated cellular calcium (Ca2+) waves. In pulmonary artery smooth muscle cells (PASMCs) nicotinic acid adenine dinucleotide phosphate (NAADP) may trigger increases in cytoplasmic Ca2+ via L-SR junctions, in a manner that requires initial Ca2+ release from lysosomes and subsequent Ca2+-induced Ca2+ release (CICR) via ryanodine receptor (RyR) subtype 3 on the SR membrane proximal to lysosomes. L-SR junction membrane separation has been estimated to be <400 nm and thus beyond the resolution of light microscopy. This study utilizes transmission electron microscopy to provide a thorough ultrastructural characterization of the L-SR junctions in PASMCs. These junctions are prominent features in these cells and we estimate that the membrane separation and extension are about 15 nm and 300 nm, respectively. We also develop a quantitative model of the L-SR junction using these measurements, prior kinetic and specific Ca2+ signal information as input data. Simulations of NAADP-dependent junctional Ca2+ transients show that the magnitude of these signals can breach the threshold for CICR via RyR3. By correlation analysis of live cell Ca2+ signals and simulated L-SR junctional Ca2+ transients, we estimate that "trigger zones" with a 60-100 junctions are required to confer a signal of similar magnitude. This is compatible with the 130 lysosomes/cell estimated from our ultrastructural observations. Most importantly, our model shows that increasing the L-SR junctional width above 50 nm lowers the magnitude of junctional [Ca2+] such that there is a failure to breach the threshold for CICR via RyR3. L-SR junctions are therefore a pre-requisite for efficient Ca2+ signal coupling and may contribute to cellular function in health and disease.

q-bio.SC↗
arXiv2009

A model for the generation of localized transient Na+ elevations in vascular smooth muscle

We present a stochastic computational model to study the mechanism of signalling between a source and a target ionic transporter, both localized on the plasma membrane (PM) and in intracellular nanometre-scale subplasmalemmal signalling compartments comprising the PM, the sarcoplasmic reticulum (SR), Ca2+ and Na+ transporters, and the intervening cytosol. We refer to these compartments, sometimes called junctions, as cytoplasmic nanospaces or nanodomains. In the chain of events leading to Ca2+ influx for SR reloading during asynchronous Ca2+ waves in vascular smooth muscle (VSM), the physical and functional link between non-selective cation channels (NSCC) and Na+/Ca2+ exchangers (NCX) needs to be elucidated in view of two recent findings: the identification of the transient receptor potential canonical channel 6 (TRPC6) as a crucial NSCC in VSM cells and the observation of localized cytosolic [Na+] transients following purinergic stimulation of these cells. Having previously helped clarify the Ca2+ signalling step between NCX and SERCA behind SR Ca2+ refilling, this quantitative approach now allows us to model the upstream linkage of NSCC and NCX. We have implemented a random walk (RW) Monte Carlo (MC) model with simulations mimicking a Na+ diffusion process originating at the NSCC within PM-SR junctions. The model calculates the average [Na+] in the nanospace and also produces [Na+] profiles as a function of distance from the Na+ source. Our results highlight the necessity of a strategic juxtaposition of the relevant signalling channels as well as other physical structures within the nanospaces to permit adequate [Na+] build-up to provoke NCX reversal and Ca2+ influx to refill the SR.

q-bio.QM↗
arXiv2007

A quantitative model for refilling of the sarcoplasmic reticulum during vascular smooth muscle asynchronous [Ca2+] oscillations

We have developed a quantitative model for the creation of cytoplasmic Ca2+ gradients near the inner surface of the plasma membrane (PM). In particular we simulated the refilling of the sarcoplasmic reticulum (SR) via PM-SR junctions during asynchronous [Ca2+] oscillations in smooth muscle cells of the rabbit inferior vena cava. We have combined confocal microscopy data on the [Ca2+] oscillations, force transduction data from cell contraction studies and electron microscopic images to build a basis for computational simulations that model the transport of calcium ions from Na+/Ca2+ exchangers (NCX) on the PM to sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) pumps on the SR as a three-dimensional random walk through the PM-SR junctional cytoplasmic spaces. Electron microscopic ultrastructural images of the smooth muscle cells were elaborated with software algorithms to produce a very clear and dimensionally accurate picture of the PM-SR junctions. From this study, we conclude that it is plausible and possible for enough Ca2+ to pass through the PM-SR junctions to replete the SR during the regenerative Ca2+ release, which underlies agonist induced asynchronous Ca2+ oscillations in vascular smooth muscle.

q-bio.QM↗
arXiv2006

Optical Studies of the coexistence curve of the n-heptane+nitrobenzene mixture near its consolute point measured by an optical method

We have measured the coexistence curve of the binary liquid mixture n-heptane+nitrobenzene near its consolute point using an optical method. In particular, the critical exponent beta describing the coexistence curve was measured for this system. Previous experimental values of beta for n-heptane+nitrobenzene were higher than the typical theoretically calculated value, an unusual, although not unique, occurrence. In an effort to study this discrepancy, we have used an improved experimental apparatus for our measurements. We have taken special care to minimize temperature gradients and maximize the temperature stability of our thermal control system. We have also exploited features of a known optical method to analyze, thoroughly, sources of systematic errors. We measured an apparent value of beta as 0.367+/- 0.006 and by a careful study of the known sources of error we find that they are not able to remove the discrepancy between the measured and the theoretical values of beta. We also measured the critical temperature of the system at Tc=291.80+/- 0.02 K (18.65 C).

cond-mat.dis-nn↗
arXiv2005

Lorentz-Lorenz Coefficient, Critical Point Constants, and Coexistence Curve of 1,1-Difluoroethylene

We report measurements of the Lorentz-Lorenz coefficient density dependence, the critical temperature, and the critical density, of the fluid 1,1-difluoroethylene. Lorentz-Lorenz coefficient data were obtained by measuring refractive index and density of the same fluid sample independently of one another. Accurate determination of the Lorentz-Lorenz coefficient is necessary for transformation of refractive index data into density data from optics-based experiments on critical phenomena of fluid systems done with different apparatus, with which independent measurement of the refractive indes and density is not possible. Measurements were made along the coexistence curve of the fluid and span the density range 0.01 to 0.80 g/cc. The Lorentz-Lorenz coefficient results show a stronger density dependence along the coexistence curve than previously observed in other fluids, with a monotonic decrease from a density of about 0.2 g/cc onwards, and an overall variation of about 2.5% in the density range studied. No anomaly in the Lorentz-Lorenz coefficient was observed near the critical density. The critical temperature is measured at Tc=(302.964+-0.002) K (29.814 C) and the measured critical density is (0.4195+-0.0018)g/cc.

cond-mat.dis-nn↗