Volume restoration in osmotically swollen lymphocytes does not involve changes in free Ca2+ concentration

An increase in cytoplasmic free [Ca²⁺], [Ca²⁺]_i, has been suggested as the trigger for the permeability changes that bring about cell volume restoration following exposure to anisotonic media. This idea was directly tested in human peripheral lymphocytes undergoing regulatory volume decrease following a hypotonic dilution of the suspension. [Ca²⁺]_i was measured with the intracellularly trapped fluorescent indicator, quin2, and showed no measurable change on hypotonic swelling or during the subsequent volume decrease. Moreover, even though the incorporated quin2 adds significant Ca-buffering to the cytoplasm, regulatory volume decrease occurred normally in the quin2-loaded cells. It appears that alterations in [Ca²⁺]_i are not involved in these processes of volume regulation. An intracellularly trapped derivative of fluorescein, bis(carboxyethyl)carboxyfluorescein, was used to monitor cytoplasmic pH, which also showed no change during regulatory volume decrease.