Intracellular ion concentrations in the frog cornea epithelium during stimulation and inhibition of Cl secretion

Abstract

The intracellular electrolyte concentrations in the isolated cornea of the American bullfrog were determined in thin freeze-dried cryosections using energy-dispersive X-ray microanalysis. Stimulation of Cl secretion by isoproterenol resulted in a significant increase in the intracellular Na concentration but did not change the intracellular Cl concentration. Similar results were obtained when Cl secretion was stimulated by the Ca ionophore A23187. Inhibition of Cl secretion by ouabain produced a large increase in the intracellular Na concentration and an equivalent fall in the K concentration. Again, no increase or decrease in the intracellular Cl concentration was detectable. Clamping of the transepithelial potential to +/- 50 mV resulted in parallel changes in the transepithelial current and intracellular Na concentration, but, with the exception of the outermost cell layer, in no changes of the Cl concentration. Only when Cl secretion was inhibited by bumetanide or furosemide, together with a decrease in the Na concentration, was a large fall in the Cl concentration observed. Application of loop diuretics also produced significant increases in the P concentration and dry weight, consistent with some shrinkage of the epithelial cells. The results suggest the existence of a potent regulatory mechanism which maintains a constant intracellular Cl concentration and, thereby, a constant epithelial cell volume. Through the operation of this system any variation in the apical Cl efflux is compensated for by an equal change in the rate of Cl uptake across the basolateral membrane. Cl uptake is sensitive to loop diuretics, directly coupled to an uptake of Na, and dependent on the Na and K concentration gradients across the basolateral membrane. Isoproterenol and A23187 seem to increase the Cl permeability of the apical membrane and thus stimulate Cl efflux. Ouabain inhibits Cl secretion by abolishing the driving Na concentration gradient for Cl uptake across the basolateral membrane.

Membrane potential difference and intracellular cation concentrations in human placental trophoblast cells in culture.

“…The intracellular Nae and K+ concentrations measured in trophoblast cells in the present study are within the range reported for epithelia (e.g. Beck et al 1980;Rick, Beck, Dorge & Thurau, 1987 (Graf, Haddad, Haeussinger & Lang, 1988 …”

Villus and Crypt Cell Composition in the Secreting Mouse Jejunum Measured with X-ray Microanalysis

“…The average Isc and Rt for these tissues immediately before freezing were 40 ± 4 A.cm −2 and 39 ± 3 ⍀.cm 2 , respectively. Overall, the composition of these cells was comparable to that seen in other epithelia (Dörge et al, 1988;Halm & Rick, 1992;Rick et al, 1987), with a low [Na] c (26.5 ± 0.6 mmol/kg wet weight), high [K] c (116.7 ± 1.2 mmol/kg wet weight) and a relatively low [Cl] c (21.8 ± 0.3 mmol/kg wet weight).…”

“…It was reasonably easy to exclude goblet and Paneth cells and, while it was not possible to identify enteroendocrine cells, they represent only 0.4% of the total cells within the epithelium (Cheng, 1974). In general the [Na]c and [K]c concentrations of the jejunal epithelial cells are comparable to those reported for other epithelia (Dörge et al, 1988;Halm & Rick, 1992;Rick et al, 1987). However, the [Cl]c is somewhat lower than that seen in other secreting epithelia.…”

“…Thus it might be expected that those cells involved in the secretory response would have an increased Na concentration due to increased influx of Na into the cells via the NaK2Cl cotransporter. Indeed, in the frog cornea (Rick et al, 1987), the stimulation of Cl secretion results in a significant increase in [Na]c with little change in [Cl]c. However, the jejunum also actively absorbs Na (Powell, 1985) and, in the absence of mucosal organic solutes such as glucose and amino acids, the dominant mechanism of Na absorption is Na/H exchange (Gunter & Wright, 1983;Turnberg et al, 1970a) which is inhibited by theophylline and other agents which stimulate Cl secretion (Nellans, Frizzell & Schultz, 1973). It is possible, therefore, that an inhibition of Na/H exchange was responsible for the reduced [Na]c of the epithelial cells following the stimulation of Cl secretion.…”

Intracellular ion concentrations and cell volume during cholinergic stimulation of eccrine secretory coil cells

“…Thus the present study was designed to directly test the latter possibility that cholinergic stimulation is associated with cell shrinkage in eccrine secretory cells. We first employed the X-ray microanalysis using the peripheral standard method (D6rge et al, 1978;Rick et al, 1987) which allows not only the change in cellular dry mass but the actual concentrations (mM) of cellular ions to be determined. We then made a limited attempt at directly determining the cell volume using collagenase-dissociated secretory coil cells under a light microscope.…”