Na(+)-Ca2+ exchange in the isolated cochlear outer hair cells of the guinea-pig studied by fluorescence image microscopy.
The outer hair cell isolated from the guinea-pig was superfused in vitro and the cytosolic calcium concentration ([Ca2+]i) and sodium concentration ([Na+]i) were measured using fluorescence indicators. Under the resting condition, [Ca2+]i and [Na+]i were 91 +/- 9 nM (n = 51) and 110 +/- 5 mM (n = 12), respectively. Removal of external Na+ by replacing with N-methyl-D-glucamine (NMDG+) increased [Ca2+]i by 270 +/- 79% (n = 27) and decreased [Na+]i by 23 +/- 4 mM (n = 6). Both changes in [Ca2+]i and [Na+]i were totally reversible on returning external Na+ to the initial value and were inhibited by addition of 0.1 mM La3+ or 100 microM amiloride 5-(N,N-dimethyl) hydrochloride. Elevation of external Ca2+ ions to 20 mM reversibly decreased [Na+]i by 8 +/- 6 mM (n = 5). Moreover, the chelation of the intracellular Ca2+ with 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA) exerted an inhibitory action on the NMDG(+)-induced reduction in [Na+]i. Exposure to 5 mM NaCN for 2 min significantly and reversibly increased [Ca2+]i by 290 +/- 37% (n = 5), but did not affect the [Ca2+]i elevation induced by the NMDG+ solution. The rise in [Ca2+]i induced by the NMDG+ solution was not enhanced by ouabain pretreatment. Addition of ouabain did not alter the [Na+]i. The present results are best explained by the presence of an Na(+)-Ca2+ exchanger in cell membrane and indicate that the activity of Na+/K+ pump is poor in outer hair cells.
Ikeda
K
K
Department of Otolaryngology, Tohoku University School of Medicine, Sendai, Japan.
Saito
Y
Y
Nishiyama
A
A
Takasaka
T
T
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D003486:Cyanides / Q000494:pharmacology; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000378:metabolism*; D008536:Meglumine / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*
D003486:Cyanides; D010042:Ouabain; D008536:Meglumine; D000584:Amiloride; D012964:Sodium; D002118:Calcium