The role of Ca2+ in volume regulation induced by Na+-coupled alanine uptake in single proximal tubule cells isolated from frog kidney

摘要

class="enumerated" style="list-style-type:decimal">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.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.An optical technique was used to examine the change in cell length induced by 5 mM L-alanine.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.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.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.The alanine-induced increases in cell length were both stereospecific and Na⁺ dependent.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.