AJP - Cell Physiology, Vol 261, Issue 2 C231-C236, Copyright © 1991 by American Physiological Society
Effects of pH on intracellular calcium levels in isolated cochlear outer hair cells of guinea pigs
K. Ikeda, Y. Saito, A. Nishiyama and T. Takasaka
Department of Otolaryngology, Tohoku University School of Medicine, Sendai, Japan.
Effects of intracellular pH (pHi) on intracellular Ca2+ (Cai2+) in the
outer hair cell (OHC) were investigated using fluorescence ratio imaging
microscopy. Cai2+ and pHi were determined with fluorescence indicators
fura-2 and 2,7-bis(2-carboxyethyl)- 5,6-carboxyfluorescein, respectively.
Intracellular alkalinization from the basal pHi of 7.22 +/- 0.03 to 7.82
+/- 0.09 (n = 7) induced by 25 mM NH4+ caused a rise in Cai2+ from 102 +/-
15 to 195 +/- 28 nM (n = 8). The elevation of Cai2+ was inhibited by
removing external Ca2+ or by 50 microM nifedipine. On the other hand, the
cytosolic acidification produced by the removal of NH4+ (delta pHi = 0.53
+/- 0.06, n = 7) and the admission of 5% CO2 (delta pHi = 0.72 +/- 0.05, n
= 4) elicited a slight reduction in Cai2+. The depolarization of the
membrane potential by exposure to 100 mM K+ induced an increase in Cai2+
that was susceptible to nifedipine, indicating the presence of
voltage-sensitive Ca2+ channels. The elevation in Cai2+ induced by 100 mM
K(+)-containing solution was increased by 138 +/- 6% (n = 4) by external
alkalinization to pH 8.4 and was decreased by 87 +/- 3% (n = 4) by external
acidification to pH 6.4. These results demonstrate that both internal and
external alkalinization of OHCs facilitate the influx of Ca2+ through the
Ca2+ channel, leading to a rise of Cai2+. Thus pH, extra- and
intracellular, may modulate the OHC motility by regulating the Cai2+.
