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M Cereijido

Publications and source records attributed to M Cereijido.

At least 73 records · Page 4Linked to original sources
PubMed1974

The sodium-transporting compartment of the epithelium of frog skin.

1. The abdominal frog skin was mounted between two chambers containing Ringer with 1 mM-Na on the outside and 115 mM-Na on the inside. When the Na concentration of the outer solution ([Na](o)) is instantaneously raised from 1 to 50 mM, the short circuit current (I) increases to a new value in less than a second, and becomes essentially time-independent. Only in a few experiments was it observed to increase further, although at a much slower rate.2. At a time t after this increase, the addition of 10(-4)M amiloride to the outer solution produces an exponential decrease of I. The area under this exponential curve is generally taken to reflect the existence of a Na- transporting compartment (NaTC).3. The amount of Na represented by NaTC is a function of t: it increases from 1.7 x 10(-9) mole. cm(-2), at t = 10 sec, to 22.8 x 10(-9) mole. cm(-2) at t = 10 min.4. In view of the fact that (a) I is not a function of the size of the ;NaTC' and (b) that whereas I reaches a steady value in a fraction of a second the size of NaTC keeps increasing for minutes, it is proposed that the ;NaTC' represents an amount of Na which is not located along the main route of transepithelial transport.5. On the assumption that the NaTC is located in a cellular compartment and that, in order to accumulate in this compartment Na should be accompanied by a permeable anion, a series of experiments were performed with Ringer in which Cl(-) was replaced by gluconate. It was observed as expected, that NaTC in gluconate is 164 times smaller than in Cl(-), but I only decreases to one half its value in Cl(-) Ringer.

Amiloride↗
PubMed1973

The effect of amiloride on sodium and potassium fluxes in red cells.

1. The effect of amiloride on the influx and efflux of (24)Na and (42)K in red cells was studied. The drug was added to the bathing Ringer or else incorporated in resealed ghosts.2. Amiloride does not inhibit the active or the passive (ouabain insensitive) extrusion of (24)Na.3. Amiloride inhibits the influx of (24)Na into red cells by 70%.4. Whether added to the inside or to the outside of the cells amiloride has no effect on the efflux of (42)K.5. Amiloride does not modify the uptake of (42)K from control Ringer. This uptake is strongly inhibited by the removal of Na. Amiloride has no effect on the extent of this inhibition.6. It is concluded that amiloride specifically inhibits the passive penetration of Na, and has no effect on the Na-K-pumping mechanism. However, at the concentration which inhibits 70% of the influx, amiloride fails to produce an observable effect on the ouabain-insensitive Na-efflux.7. On the basis that the information obtained could be extrapolated to other membranes, the effect of amiloride on epithelial membranes is discussed.

Amiloride↗
PubMed1971

The effect of antidiuretic hormone on Na movement across frog skin.

1. The effect of antidiuretic hormone (ADH) on the movement and distribution of Na was studied. This was done using three different approaches: (a) the measurement of Na and (22)Na in slices of epithelium of skins which were exposed to Ringer of varied composition containing (22)Na, (b) the measurement of the influx of Na from the outer to the inner bathing solution with (22)Na added to the outside, and (c) the use of a recently introduced technique which permits the direct evaluation of the flux from the outer solution --> epithelium, (J(OT)), i.e. the flux across the barrier which is generally regarded as the site of ADH activity.2. ADH increased the influx from the outer to the inner bathing solution of Na (50%) not only when the concentration of Na on the outside was 115 mM (i.e. higher than in the epithelium) but even when the concentration was 1 mM (67%).3. When the skin was bathed with 1mM-Na Ringer on the outside, ADH increased the unidirectional Na flux J(OT) by 56% (Rana pipiens) and 71% (Leptodactylus ocellatus). When the concentration was 115 mM a small increase (17%) was observed in paired skins of R. pipiens. Under this condition no change was observed in L. ocellatus.4. The amount of epithelial sodium which is labelled by (22)Na added to the outside was taken to reflect the amount of Na involved in Na transport across the epithelium. Depending on whether the concentration of Na on the outside was high (115 mM) or low (1 mM), ADH produced an increase, or a decrease, of both the total Na content and the amount of (22)Na exchanged.5. When the concentration of Na on the outside was low, ADH increased the total influx and J(OT) in spite of the fact that it lowers the total Na content and does not affect the exchangeable pool of Na. This observation is inconsistent with the view that the effect of ADH is due to the fact that the increased permeability of the outer barrier allows more Na into the cell, and that the resulting increase of Na concentration in the cytoplasm accelerates the Na pumps at the inner side of the cells.6. It is concluded that ADH speeds up Na movements at the outward facing barrier, and that this exchange which facilitates the penetration of Na into a transporting compartment produces also a gain or a loss of Na in compartments not directly involved in Na transport across the epithelium. One compartment which is not involved in Na transport might be the cytoplasm of the epithelial cells.

Animals↗
PubMed1970

The penetration of sodium into the epithelium of the frog skin.

The aim of this paper is twofold. First, to describe a method for the measurement of the unidirectional flux of Na from the outer bathing solution into epithelium (J(OT)), and second, to describe the use of this method under a variety of experimental conditions in order to obtain some insight into the nature of this flux. The method developed is based on the exposure of a frog skin to a Ringer solution containing (22)Na. The exposure is made so that neighboring points along the surface remain in contact with the (22)Na solution for gradually longer periods, ranging from 0 to 46 sec. Some 8 to 10 samples of the exposed part are used to obtain the time course of the uptake of (22)Na and this time course is used, in turn, to evaluate J(OT). This flux is then studied in skins mounted between two identical Ringer solutions with 115 mM Na (11.25 +/- 0.10 [18] micromole.hr(-2) cm(-2)), and in skins mounted with Ringer with 1 mM Na on the outside and 115 mM Na on the inside (0.43 +/- 0.05 [18] micromole.hr(-1).cm(-2). From the observations that the flux is much larger than the net Na flux across the whole skin, that it is inhibited by K(+), and is unaffected by ouabain, it is concluded that the penetration of Na(+) into the epithelium does not occur by simple diffusion and is not directly dependent on an ouabain-sensitive mechanism. In the course of these experiments it was observed that when the skin was crushed between two chambers the uptake of Na in the neighboring exposed areas was decreased.

Animals↗
PubMed1968

The effect of sodium concentration on the content and distribution of sodium in the frog skin.

1. The content and distribution of sodium in the epithelium of the frog skin (Leptodactylus ocellatus L.) have been studied.2. The inulin space, the (22)Na exchange, and the amounts of water and sodium were measured in samples of connective tissue. The results indicate that the necessary assumptions generally made to calculate the sodium and water contents of the epithelial cells as the difference between the total content in the tissue and the amounts contained in the inulin space are not valid in the frog skin.3. The mean concentration of sodium in the epithelium has been obtained from direct measurements of sodium and water in samples of epithelium. To measure the water content of the epithelium a new technique has been developed. When the skin is bathed with Ringer solution containing 115 mM-Na on both sides, the mean concentration of sodium in the epithelium is 79 mM. When the concentration of sodium in the Ringer is 1 mM the mean concentration in the epithelium is 25 mM. When the skin is bathed with Ringer with 1 mM-Na on the outside and 115 mM-Na on the inside-a situation which resembles the natural condition in the skin-the mean concentration of sodium in the epithelium is 52 mM.4. The compartmentalization of Na was studied by comparing the sodium content and the degree of exchange with (22)Na in the bathing solutions. In these experiments the skins were exposed to Ringer solutions with different concentrations of sodium, and (22)Na on one or both sides.5. The results indicate that the epithelium has a compartment of sodium which is not exchangeable in 40-80 min and whose size is not appreciably changed by a threefold change in the Na content in the epithelium and a hundredfold change in the concentration of the bathing solution.6. Sodium exchangeable in 40-80 min seems to be contained in two different compartments: (a) a large one that contains fixed sodium is mainly connected to the inside, and does not appear to participate directly in sodium transport across the frog skin; (b) a small one, that is bounded on the inside by a Na-impermeable barrier, and that seems to comprise the sodium involved in active transport. When the skin is bathed with Ringer solutions with 115 mM-Na on the inside and 1 mM-Na on the outside, the transporting compartment contains some 13% of the total sodium in the epithelium.7. The results are interpreted on the basis of a model recently proposed by Cereijido & Rotunno (1968). The major feature of this model is that the sodium transporting compartment is confined to the plasma membrane of the epithelial cells.

Animals↗
PubMed1967

Transport and distribution of sodium across frog skin.

1. The time course of (22)Na influx across frog skin mounted as a flat sheet between two lucite chambers has been studied. The flux reaches its maximal steady value in about 30 min.2. The time course of changes in (22)Na specific activity in the cells has been followed by two different methods: (1) periodical measurements of (22)Na activity in pieces of skin mounted in a special device in which the outer facing membrane was in contact with the tracer and (2) measurement of uptake of (24)Na in individual pieces of skin suspended in Ringer solution. Under both circumstances the skin failed to exchange all its Na.3. Considerations on the basis of the kinetics of (22)Na influx and (22)Na specific activity indicate that there exist at least two different Na compartments in the epithelium, one of them being directly involved in Na transport.4. The (22)Na specific activity profile was studied in skins which had previously been mounted as a flat sheet between two chambers with tracer in one of them. This was carried out by removing the skin from the chamber, freezing, slicing and analysing the slices for Na and (22)Na. The results indicate that both Na compartments are distributed across the whole epithelium.5. The results of these studies are taken to indicate: (a) that the Na partition in the tissue is not a result of the Na being contained in different cellular layers; (b) that Na transport across frog skin is carried out by all the epithelial cells and is not restricted to those of a particular layer; (c) that Na entry from an outer solution containing from 1 to 10 mM-Na occurs into the transporting cells down an electrochemical potential gradient and therefore need not involve an active mechanism at the outer border of the cells.

Animals↗