title: The role of Ca2+ in volume regulation induced by Na+-coupled alanine uptake in single proximal tubule cells isolated from frog kidney.
abstract: 1. It has been suggested that epithelial cells maintain cell volume and function, in the face of changes in the rate of transepithelial transport, by activation of volume-regulatory pathways. 2. The aim of the following study was to examine directly the effect of an alteration in Na+-coupled alanine transport on cell length in single proximal tubule cells isolated from frog kidney. 3. An optical technique was used to examine the change in cell length induced by 5 mM L-alanine. 4. On addition of L-alanine to the bath there was an initial increase in cell length to a peak value. This was followed by two types of response. In eighteen out of thirty-one cells a typical volume-regulatory response was observed. The remaining cells showed no volume regulation. 5. Volume regulation was not affected by the removal of extracellular Ca2+. The mean degrees of recovery were 159 +/- 21 % (n = 18) and 144 +/- 18 % (n = 8) in the presence and absence of Ca2+, respectively. 6. Volume regulation was inhibited by depletion of intracellular Ca2+ stores, or in the presence of either Gd3+ or DIDS. The mean degrees of regulation were 55.4 +/- 9.2 % (n = 7), 68.2 +/- 18.8 % (n = 7) and 69.1 +/- 14.3 % (n = 7), respectively. 7. The alanine-induced increases in cell length were both stereospecific and Na+ dependent. 8. The evidence suggests that volume regulation induced by Na+-coupled alanine uptake may be dependent on the release of Ca2+ from intracellular stores. This is in contrast to volume regulation induced by hypotonic shock, which appears to require extracellular Ca2+. Results obtained using a hypotonic shock should, therefore, be viewed with caution.
authors.affiliation: Department of Biomedical Science, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: P R
authors.initials: PR
authors.lastname: Mounfield
authors.forename: L
authors.initials: L
authors.lastname: Robson
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000409:Alanine / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002469:Cell Separation; D005682:Gadolinium / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011896:Rana temporaria; D012964:Sodium / Q000502:physiology*; D013237:Stereoisomerism; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D002110:Caffeine; D019284:Thapsigargin; D012964:Sodium; D005682:Gadolinium; D000409:Alanine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium