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ABSTRACT: The details of our previously described theory of how the endothelium controls corneal hydration in the absence of the epithelium are provided. A central postulate is that the endothelium can produce across its limiting plasma membranes an osmotic gradient that reduces stromal swelling pressure so that it does not exceed intraocular pressure during thinning of a swollen cornea.
American journal of optometry and physiological optics 08/1977; 54(7):439-44.
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ABSTRACT: The efflux of Mg++ from squid axons subject to internal solute control by dialysis is a function of ionized [Mg], [Na], [ATP], and [Na]o. The efflux of Mg++ from an axon with physiological concentrations of ATP, Na, and Mg inside into seawater is of the order of 2-4 pmol/cm2s but this efflux is strongly inhibited by increases in [Na]i, by decreases in [ATP]i, or by decreases in [Na]o. The efflux of Mg++ is largely independent of [Mg]i when ATP is at physiological levels, but in the absence of ATP reaches half the value of Mg efflux in be presence of ATP when [Mg]i is about 4 mM and [Na] 40 mM. Half-maximum responses to ATP occur at about 350 micronM ATP into seawater with Na either present or absent. The Mg efflux mechanism has many similarities to the Ca efflux system in squid axons especially with respect to the effects of ATP, Nao, and Na on the flux. The concentrations of free Mg and Ca in axoplasm differ, however, by a factor of 10(5) while the observed fluxes differ by a factor of 10(2).
The Journal of General Physiology 05/1977; 69(4):389-400. · 3.84 Impact Factor
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The Alabama journal of medical sciences 05/1976; 13(2):196-205.
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ABSTRACT: Ca efflux in dialyzed squid axons was measured with 45Ca as a function of internal ionized Ca in the range 0.005-10 muM. Internal Ca stores were depleted by treatment with CN and dialysis with media free of high energy compounds. The [Ca]iota was stabilized with millimolar concentrations of EDTA, EGTA, or DTPA. Nonspecific leak of chelated Ca was measured with [14C]-EDTA and found to be 0.02 pmol/cm2s/mM EDTA. Correction of the measured Ca efflux for this leak of chelated calcium was made when appropriate. Ca efflux was roughly linear with internal free Ca in the range 0.005-0.1 muM. Above 0.1 muM, efflux was less than proportional to concentration but did not saturate at the highest concentration studied. Ca efflux was reduced about 50% by replacement of external Na with Li at Caiota approximately 1 muM, but was insensitive to such replacement for Ca less than 0.1 muM. Ca efflux was insensitive to internal Mg in the range 0-4 mM, indicating that the Ca pump favors Ca over Mg by a factor of about 10(6). Ca efflux was reduced about 60% by increasing internal Na from 1 to 80 mM. This effect could represent weak interference of a Ca carrier by Na or a loss of driving force because of a reduction in ENa - Em occasioned by an increase in Naiota. A few measurements were made of Ca influx in intact and in dialyzed fibers. In both cases, Ca influx increased when external Na was replaced by Li.
The Journal of General Physiology 09/1975; 66(2):223-50. · 3.84 Impact Factor
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ABSTRACT: 45Ca and 14C-labeled ethylenediamine-N, N'-tetraacetic acid (EDTA) effluxes were measured in internally dialyzed barnacle muscle fibers. In 45Ca experiments the internal ionized 45Ca was fixed at 0.2 muM with ethyleneglycolbis-(beta-aminoethylether)-N, N'-tetraacetic acid(EGTA). The 45Ca efflux was found to increase with internal CaEGTA from 0.05 pmol/cm2.s(CaEGTA equal to 0.02 mM) to 5.0 pmol/cm2.s(CaEGTAequal to 9.6 mM). To determine whether or not most of this increase in efflux was due to the exit of undissociated CaEGTA, comparable experiments were performed with Ca-[14-C]EDTA. Over the same range of internal calcium as studied in the 45Ca experiments, the Ca-[14-C]EDTA efflux was no more than 12% of the 45Ca efflux. We conclude that the exit of undissociated 45Ca cannot account for most of the 45Ca efflux nor can it account for the dependence of 45Ca efflux on internal CaEGTA. The experiments also demonstrated the existence of an endogenous pool of calcium, of 0.43 mmol/kg (about half the total calcium), which remained unexchanged during dialysis.
Biophysical Journal 04/1975; 15(3):281-6. · 3.65 Impact Factor
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The American journal of physiology 07/1973; 224(6):1254-9.
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Journal of Theoretical Biology 07/1970; 27(3):433-53. · 2.21 Impact Factor
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The American journal of physiology 04/1969; 216(3):536-41.
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ABSTRACT: With an in vitro chamber method experiments were performed to determine the relative ionic conductances of the nutrient membrane (membrane facing muscularis mucosa). The concentration of a given ion in the nutrient bathing solution was changed, and the ensuing time course of the change in transmucosal potential difference (PD) was recorded. Changing K(+) from 4 to 79 mM produced a response in PD which occurred markedly faster than the response for the reverse change, and similar results were obtained by changing the Cl(-) concentration. It was found that these differences were predicted by the analysis of an idealized model consisting of a membrane in series with a diffusion barrier. When both the K(+) and Cl(-) were changed, such that the product of their concentrations remained constant, the time courses of the responses were again similiar to those predicted on the basis of the model. From the magnitudes of the total PD responses it is shown that in the presence of a 4 mM K(+) nutrient solution, the conductivity of the nutrient membrane appears to be entirely due to the K(+) and Cl(-) conductances, the K(+) conductance being about twice that of the Cl(-). It is also shown that with a 79 mM K(+) nutrient solution the parameters of the membrane were changed such that the conductances of the two ions were approximately equal. The time constant for diffusion of KCl or NaCl across the barrier consisting of the submucosa, muscularis mucosa, and lamina propria is about 1 min.
Biophysical Journal 12/1968; 8(11):1211-27. · 3.65 Impact Factor
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ABSTRACT: With an in vitro chamber method experiments were performed to determine the relative ionic conductances of the nutrient membrane (membrane facing muscularis mucosa). The concentration of a given ion in the nutrient bathing solution was changed, and the ensuing time course of the change in transmucosal potential difference (PD) was recorded. Changing K+ from 4 to 79 mM produced a response in PD which occurred markedly faster than the response for the reverse change, and similar results were obtained by changing the Cl- concentration. It was found that these differences were predicted by the analysis of an idealized model consisting of a membrane in series with a diffusion barrier. When both the K+ and Cl- were changed, such that the product of their concentrations remained constant, the time courses of the responses were again similiar to those predicted on the basis of the model. From the magnitudes of the total PD responses it is shown that in the presence of a 4 mM K+ nutrient solution, the conductivity of the nutrient membrane appears to be entirely due to the K+ and Cl- conductances, the K+ conductance being about twice that of the Cl-. It is also shown that with a 79 mM K+ nutrient solution the parameters of the membrane were changed such that the conductances of the two ions were approximately equal. The time constant for diffusion of KCl or NaCl across the barrier consisting of the submucosa, muscularis mucosa, and lamina propria is about 1 min.
Biophysical Journal.
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ABSTRACT: Under most conditions the osmotic gradient hypothesis can account for water movement in the stomach. However, in the resting in vivo dog stomach, with isotonic HCl bathing the mucosal surface, H+ disappears and Na+ appears at approximately the same rate and water moves from the blood to the mucosal bathing fluid, resulting in the production of a hypotonic fluid. In the present paper we have developed a conceptual model to explain these findings. According to the model the cells on the surface and those lining the pits are impermeable to both water and solutes, the site of the H+-Na+ exchange is the tubules, and the tubules are permeable to water. In demonstrating how the model works we have first obtained expressions for the concentration profiles of the ions in the pits under conditions of no water flow and show that the fluid at the bottom of the pits would be hypertonic. We then allow the tubules to become permeable to water, with the result that water moves from blood to lumen while the number of osmotically active particles does not change (the loss of H+ equals the gain of Na+). We obtain an approximate quantitative picture during water flow by making the assumption that HCl and NaCl diffuse independently.
Journal of Theoretical Biology.
