Effects of pH on intracellular calcium levels in isolated cochlear outer hair cells of guinea pigs.
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+.
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; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology; D002469:Cell Separation; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012996:Solutions
D015220:Calcium Channels; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D000584:Amiloride; D006859:Hydrogen; D009543:Nifedipine; D011188:Potassium; D002118:Calcium