Microprobe analysis in studies and diagnosis of cystic fibrosis

The resting membrane potential of cells are measures of electrical work, not of ionic currents

Living cells create electric potential force, E, between their various phases by at least three distinct mechanisms. Charge separation, F = [equation: see text] (Eqn 1) creates the potential, E = [equation: see text] of -120 to -145 mV between cytoplasmic and mitochondrial phases by unbalanced proton expulsion powered by the redox energy of the respiratory chain. Electrically unbalanced flow of Na+ through voltage gated Na+ channels raises the potential of nerve from -85 to +30 mV. The so-called resting potential of cells, which varies from -85 mV in heart to -4.5 mV in red cell, does not appear to result from the unbalanced flow of ions between phases, but rather to be a measure of the work required to move ions between phases. Movement of an ion between phases entails three types of energy. Concentration work is that required to move an ion between phases containing different concentrations of ions: [equation: see text] Electrical work is that work required to move an ion from phases with differing electric potentials: [equation: see text] The Nernst potential of an ion existing at different concentrations in two phases is: [equation: see text] The osmotic work term is small and can generally be ignored. In heart the measured resting potential between extra- and intracellular phases, EN is approximately -85 mV. The calculated Nernst potential of K+, E [K+]out/in, is -85 mV (Eqn 4). This means that in heart, K+ distributes itself between the two phases as if it moved through an open ion channel. Its concentration work (Eqn 2) is equal in magnitude but opposite in sign to its electrical work (Eqn 3). This makes net K+ current flow, I, equal 0, indicating that this potential cannot be a diffusion potential. In liver the resting potential ranges from -28 to -40 mV, and is equivalent to the E[Cl-]out/in, while in red cell the resting potential is about -4.5 mV, which is equivalent to the potential of all nine major inorganic ion species except Na+, K+ and Ca2+. Therefore the resting potential between extra- and intracellular phases of cells should be thought of, not as a diffusion potential but rather as a measure of the electrical work: [equation: see text] required to transport the most permeant ions in a Gibbs-Donnan near-equilibrium system, either K+ or Cl- or both, between the phases of an aqueous system during the flow of current required to measure potentials with intracellular KCl electrodes or during ion movements brought about during normal cellular activity. The resting electrical potential results from the existence of a mono-ionic Gibbs-Donnan near-equilibrium system between the extra- and intracellular phases of cell wherein the activity of free H2O within all phases of the system is equal and the energy of the gradients of the nine major inorganic ions, delta G[ionz]out/in, are in near-equilibrium with one another, with the potential between the phases, EN, and with the energy of ATP hydrolysis. delta GATP Hydrolysis. ranges from a low of -55 to slightly over -60 kJ/mole in all cell types.(ABSTRACT TRUNCATED AT 400 WORDS)

Alterations in specific activity of lysosomal alpha-glucosidase in cystic fibrosis

Cultured skin fibroblasts derived from patients with cystic fibrosis contain 2.1-fold more acid alpha-glucosidase (EC 3.2.1.3) than normal fibroblasts. This difference is amplified to 2.3-fold when the cells are extracted in Triton X-100. In a study of 14 fibroblast cell lines derived from CF homozygotes and heterozygotes, normal individuals and patients with other recessively inherited disorders, normal individuals could be distinguished from either CF homozygotes or heterozygotes based on the ratio of acid alpha-glucosidase to beta-hexosaminidase when fibroblasts were extracted in either water or Triton X-100. However, the best distinction could be made with water extracts as there was no overlap among individual data points in the three categories. The acid to neural alpha-glucosidase ratio only distinguished CF homozygotes from normal individuals when cells were extracted in Triton X-100. The use of a ratio relationship of acid alpha-glucosidase with beta-hexosaminidase allows the comparison of data from multiple experiments on different days of assay and on cells at different passage numbers. These results suggest that alpha glucosidase may have a role in the primary defect in cystic fibrosis.

The chronically pilocarpine-treated rat in the study of cystic fibrosis: investigations on submandibular gland and pancreas

The chronically pilocarpine-treated rat has been proposed as an animal model for the disease cystic fibrosis, a generalized exocrinopathy. The effect of chronic pilocarpine treatment on structure, composition, and function of the acinar cells of rat submandibular gland and pancreas was investigated by electron microscopy, X-ray microanalysis, and biochemical analysis. The morphological effects of chronic pilocarpine treatment were most pronounced in the pancreas. The number and size of the zymogen granules was increased, and the granules had a less electron-dense appearance. X-ray microanalysis at the cellular level showed in both the submandibular gland and the pancreas a significant increase in calcium and a decrease in sodium. The increase in cellular calcium concentrations can be explained by an increase in the relative volume of secretory material in the cell (assessed by morphometry) and an increase in the local calcium concentration in the secretory material (assessed by X-ray microanalysis at the subcellular level). Chronic pilocarpine treatment caused a disturbance of glycolysis and energy metabolism in the submandibular gland, but no significant effects in this respect were noted in the pancreas. On the other hand, a nearly twofold increase of the pancreatic amylase activity was noted. The pancreas appeared somewhat hyperreactive towards cholinergic stimulation.