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1 Central Clinical Laboratory2 Department of Internal Medicine3 Department of Physiology, and Osaka Medical College, Takatsuki 569-8686, Japan
The effects of intracellular Ca2+ concentration, [Ca2+]i, on the volume of rat alveolar type II cells (AT-II cells) were examined. Perfusion with a Ca2+-free solution induced shrinkage of the AT-II cell volume in the absence or presence of amiloride (1 µM, an inhibitor of Na+ channels); however, it did not in the presence of 5-(N-methyl-N-isobutyl)-amiloride (MIA, an inhibitor of Na+–H+ exchange). MIA decreased the volume of AT-II cells. Inhibitors of Cl––HCO3– exchange, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) also decreased the volume of AT-II cells. This indicates that the cell shrinkage induced by a Ca2+-free solution is caused by a decrease in NaCl influx via Na+–H+ exchange and Cl––HCO3– exchange. Addition of ionomycin (1 µM), in contrast, induced cell swelling when AT-II cells were pretreated with quinine and amiloride. This swelling of the AT-II cells is not detected in the presence of MIA. Intracellular pH (pHi) measurements demonstrated that the Ca2+-free solution or MIA decreases pHi, and that ionomycin increases it. Ionomycin stimulated the pHi recovery after an acid loading (NH4+ pulse method), which was not noted in MIA-treated AT-II cells. Ionomycin increased [Ca2+]i in fura-2-loaded AT-II cells. In conclusion, the Na+–H+ exchange activities of AT-II cells, which maintain the volume and pHi, are regulated by [Ca2+]i.
(Received 17 August 2004;
accepted after revision 10 November 2004; first published online 7 January 2005)
Corresponding author T. Nakahari: Department of Physiology, Osaka Medical College, Takatsuki, 569-8686, Japan. Email: takan{at}art.osaka-med.ac.jp
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