Regulatory volume increase in rat lacrimal gland acinar cells

The volume of acinar cells isolated from rat lacrimal glands was measured during hypertonic shock. Cells shrank in hypertonic solutions, but a regulatory volume increase (RVI) was only observed under certain conditions. In HEPES-buffered solutions at 37 degrees C, an RVI was observed. This was inhibited by 20 microM bumetanide, an inhibitor of Na(+)-K(+)-2Cl- cotransport. RVI did not occur in HEPES-buffered solutions at 20 degrees C suggesting that Na(+)-K(+)-2Cl- cotransport is inactive at this temperature. In HCO3- buffered solutions however, an RVI was observed at 20 degrees C. In these conditions, the RVI was inhibited by 500 microM 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid (H2-DIDS) and 10 microM 5-(N-methyl-N-isobutyl)-amiloride (MIBA) indicating the involvement of Cl(-)-HCO3- exchange and Na(+) -H+ exchange respectively. RVI was also supported by a mixture of neutral amino acids, and by the nonmetabolizable amino acids 5 mM alpha-(methylamino)isobutyric acid (MeAIB) and 5 mM alpha-aminoisobutyric acid (AIB). These data suggest that the accumulation of amino acids, possibly by the system A Na(+)-coupled amino acid cotransporter, contributes to RVI in these cells. In conclusion, rat lacrimal gland acinar cells are capable of undergoing RVI following shrinkage by hypertonic shock.