PubMed · 9341633
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P S Mehler. 1997-10-15. Long QT interval.. https://pubmed.ncbi.nlm.nih.gov/9341633/
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Cochlear marginal cells and vestibular dark cells transport potassium into the inner ear endolymph, a potassium-rich fluid, the homeostasis of which is essential for hearing and balance. We have formulated an integrated mathematical model of ion transport across these epithelia that incorporates the biophysical properties of the major ion transporters and channels located in the apical and basolateral membranes of the constituent cells. The model is constructed for both open- and short-circuit situations to test the extremes of functional capacity of the epithelium and predicts the steady-state voltages, ion concentrations, and transepithelial currents as a function of various transporter and channel densities. We validate the model by establishing that the cells are capable of vectorial ion transport consistent with several experimental measurements. The model indicates that cochlear marginal cells do not make a significant direct contribution to the endocochlear potential and illustrates how changes to the activity of specific transport proteins lead to reduced K(+) flux across the marginal and dark cell layers. In particular, we investigate the mechanisms of loop diuretic ototoxicity and diseases with hearing loss in which K(+) and Cl(-) transport are compromised, such as Jervell and Lange-Nielsen syndrome and Bartter syndrome, type IV, respectively. Such simulations demonstrate the utility of compartmental modeling in investigating the role of ion homeostasis in inner ear physiology and pathology.
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The story, described here in detail, started in 1962 with the publication of a seminal paper by Frederic Bartter et al. in the December issue of the American Journal of Medicine. The authors reported two pediatric patients with hitherto undescribed features, namely growth and developmental delay associated with hypokalemic alkalosis and normal blood pressure despite high aldosterone production. It soon became clear that this condition was not so exceptional. The syndrome named after Bartter was actually identified in children as well as in adults, females as well as males and in all five continents. It took almost four decades to clarify the exact nature of the disease. Bartter disease is an autosomal recessive disorder with four genotypes and mainly two phenotypes. Moreover, there are acquired secondary forms of Bartter syndrome as well as pseudo-Bartter syndromes. The history demonstrates the power of genetics but also illustrates the fundamental and irreplaceable contributions from nephrologists and renal physiologists.