1,721,256 research outputs found
Measurements of electrical parameters of frog skin "in situ" as a function of environmental parameters
No full textElectrical parameters of the abdominal skin of the pithed frog (Rana esculenta) can be measured by means of a couple of double coaxial electrodes /1,2,3/. One of the double electrodes is inserted into the ventral lymphatic sac of the frog, between skin and muscles, and the second is placed in front of this, on the outer surface of the skin. The inner electrode of the coaxial pair measures the skin potential difference (pd), while the outer delivers a countercurrent, for modifying the pd. By this method, pd, short circuit current and skin DC resistance have been determined as a function of temperature (5 to 40 °C) and of pH (4 to 9) on the same living animal. The behaviour of the substrate bears both qualitative and quantitative similarities with the isolated skin in the lower temperature range, but no transport maximum exists around 27 °C /4/. The pH dependence of electrical parameters is also quite different than in the isolated substrate /5/. 1. G. Torelli, F. Celentano, G. Cortili, G. Guella: Boll. Soc. It. Biol. Sper. 44, 501 (1967); 2. F. Celentano, G. Cortili, G. Guella, G. Torelli: Boll. Soc. lt. Biol. Sper. 44, 504 (1967); 3. M. Bianchi, G. Torelli, F. Celentano, G. Cortili: Boll. Soc. It. Biol. Sper. 45, 385 (1968); 4. G.A. Poster: Biochim. Biophys. Acta 211, 487 (1970); 5. E. Schoffeniels: Arch. Int. Physiol. Biochim. 53, 513 (1955)
Phenomenological description of selectivity in actively transporting membranes
No full textA phenomenological description of active and passive flows of solute and solvent across a biological membrane can be made explicitly considering the dependence of matter flows upon the rate of metabolic reactions /1/, or introducing a generalized chemical potential including a term accounting for active transport /2/, or making the hypothesis that solute flow can be splitten in two superimposed and thermodynamically couplet active and passive components. With the two latter approaches, by means of a transformation of flows and forces at constant temperature and in absence of electric field, two systems of three interacting flows, sustained by three different forces, can be obtained. The two systems lead to equivalent descriptions of volumetric flow and allow the determination of the reflection coefficient for solute passive transport /3/. The relationship between reflection coefficient and apparent reflection coefficient /4/ is also obtained. 1. A. Katchalsky, P. F. Curran. Nonequilbrium Thermodynamics in Biophysics, Cambridge Mass. (1965); 2. J. M. Diamond. J. Physiol. 161, 503 (1962); 3. F. Celentano, G. Monticelli, G. Torelli. Proc. Ist. Europ. Biophys. Congr. 3, 309 (1971); 4. C. J. Bentzel, M. Davies, W. N. Scott, M. Zatzman, A. K. Solomon. J. Gen. Physiol. 51, 517 (1968
Pedley (J. G.) - Torelli (M.). The Sanctuary of Santa Venera at Paestum. Il santu- ario di Santa Venera a Paestum.
No full textVan Wonterghem Frank. Pedley (J. G.) - Torelli (M.). The Sanctuary of Santa Venera at Paestum. Il santu- ario di Santa Venera a Paestum.. In: Revue belge de philologie et d'histoire, tome 75, fasc. 1, 1997. Antiquite - Oudheid. pp. 245-246
Analysis of NaC1 permeability in rabbit gall-bladder
No full textIn rabbit gall-bladder NaC1 is both actively and passively transported. A phenomenological description of solute and solvent (water) active and passive flows across a biological membrane can be made explicitly considering the dependence of matter flows upon the rate of metabolic reactions, or introducing a generalized chemical potential including a term accounting for active transport, or making the hypothesis that solute flow can be splitten in two superimposed and thermodynamically coupled active and passive components. By the latter approach, by means of transformation of flows and forces at constant temperature and in absence of electric field, it was obtained for volumetric flow (Jv): Jv = LpΔp+LpdΔπ+LpaXa where Δp, Δπ, Xa are respectively the hydrostatic pressure difference, the osmotic pressure difference and a force related to active transport. Lp, Lpd and Lpa are the phenomenological coefficients. This equation can be experimentally tested
Sodium chloride reflection coefficient in rabbit gall bladder
No full textBy means of the Kedem-Katchalsky thermodynamic description of active transport, a relationship has been derived between the apparent reflection coefficient and the Staverman reflection coefficient for passive transport of a solute which is both actively and passively transported. The relationship between volumetric flow and its driving forces, containing the Staverman reflection coefficient, was tested for sodium chloride in rabbit gall bladder and the reflection coefficient was evaluated
Some remarks about reflection coefficient
No full textBiological membranes selectivity for solutes is measured by the reflection coefficient σ, defined as σ = (ΔP/Δπ)Jv=0 where ΔP is the hydrostatic pressure difference required to zero the volumetric flow Jv driven by an osmotic pressure difference Δπ of the considered solute. It as been shown by means of non-equilibrium thermodynamics that σ = (-LPD/LP) where LP and LPD are filtration and ultrafiltration coefficients. Now, if the permeating nonelectrolyte is also actively transported by the membrane, volumetric flow is given by Jv = LPΔP + LPDΔπ + LPAYA where YA is a force sustaining active transport and LPA the phenomenological coefficient, coupling that force to volumetric flow. In Kedem and Katchalsky treatment YA is the affinity of the chemical reaction sustaining active flux, while Diamond proposed the introduction of an active transport potential with the characteristics of a chemical potential. Other proposals can be made, but the definition of YA is not important for subsequent treatment
Valutazione statistica della dipendenza lineare del flusso volumetrico dalle forze che lo sostengono
No full textSulla base di risultati preliminari ottenuti sulla cistifellea di coniglio, si è proposto di interpretare l’andamento del flusso volumetrico (Jv) mediante un modello basato sulla termodinamica dei fenomeni irreversibili lineari, ottenendo la relazione Jv = LpDPi + LpdDP + LpsYs dove DPi e DP sono le differenze di pressione osmotica di un soluto impermeante e di quello trasportato (NaCl), Ys una forza che sostiene il trasporto attivo, Lp, Lpd ed Lps i coefficienti fenomenologici di filtrazione, ultrafiltrazione ed accoppiamento con la forza Ys. Se si opera in condizioni in cui il prodotto LpsYs è costante, la relazione sopra scritta rappresenta un piano nello spazio (DPi, DP, Jv). Dall’analisi della regressione multipla in 18 organi (145 terne sperimentali) risulta ora che è possibile interpolare i punti mediante un piano con un livello di significatività migliore dell’1% in 15 casi e del 5% in 3 casi. Fenomeni di osmosi non lineare potrebbero però rendere possibile l’interpolazione dei dati con una superficie curva pur lasciando una buona significatività nell’interpolazione con un piano. Si è perciò eseguito un test di coincidenza dei piani determinati da punti con Jv positivo e Jv negativo, dal quale è risultato che i due piani non sono significativamente diversi. Inoltre la costanza di LpsYs nel tempo è stata verificata, oltre che con controllo nel corso dell’esperimento, anche verificando la non significatività delle differenze tra i coefficienti di riflessione s = -Lpd/Lp calcolati con gruppi di 7 punti all’inizio (A), a metà (B), alla fine (C) dell’esperienza e con tutti i punti: sA = 0,59 ± 0,06, sB = 0,73 ± 0,13, sC = 0,57 ± 0,05, (9 esp), s = 0,60 ± 0,04 (18 esp). Si è inoltre determinato indipendentemente il coefficiente di filtrazione Lp = 0,507 ± 0,059*10-11 cm3/dine s che, per DPi elevate (oltre 100 mM/1 saccarosio) diviene L’P = 0,124 ± 0,041*10-11 cm3/dine s
Volumetric flow across frog skin "in vitro"
No full textVolumetric flow Jv across a membrane depends on several variables, one of them being hydrostatic pressure difference ΔP which can be simulated by the osmotic pressure difference of an impermeant solute Δπi = ΔP. In the present communication we describe the dependence of Jv upon Δπi in sacs made with the leg skin of Rana esculenta bathed in phosphate Ringer pH 7 at 20 °C. The impermeant solute (sucrose) was added only in the external perfusing solution while the inside solution was changed after each flow measurement to avoid any significant composition change. Volumetric flow was measured gravimetrically as in the case of gall bladder
Coefficiente di riflessione di un soluto trasportato attivamente da una membrana
No full textLa selettività di una membrana ad un soluto trasportato passivamente è definita dal coefficiente di riflessione σ = (ΔP/Δπ)Jv=0. Per membrane che presentano anche un trasporto attivo di soluto è stato introdotto il coefficiente σapp definito in modo analogo. Quest’ultimo però varia con le condizioni sperimentali come risulta dalle seguenti considerazioni. Presupponendo che forze distinte sostengano direttamente i flussi attivo e passivo di soluto, la funzione di dissipazione può essere rappresentata come funzione della differenza di pressione idrostatica ΔP, della differenza di pressione osmotica Δπ e da una forza attiva Ys non ben identificata
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