Chen C, Nenov A, Norris C H, Bobbin R P
Kresge Hearing Research Laboratory of the South, Department of Otorhinolaryngology and Biocommunication, Louisiana State University Medical Center, New Orleans 70112-2234, USA.
Hear Res. 1995 Jun;86(1-2):25-33. doi: 10.1016/0378-5955(95)00050-e.
Ca2+ channel currents and their modulation by adenosine 5'-triphosphate (ATP) in acutely isolated guinea pig outer hair cells (OHCs) were investigated using the whole-cell patch-clamp technique. The current-voltage (I-V) relation of OHCs indicated that the Ca2+ channel opened near -30 mV, and the current reached a maximum at +10 and 0 mV in 20 mM Ca2+ and Ba2+ external solutions, respectively. BayK 8644 (BayK, 2 microM) caused a 3.5-fold increase in peak Ca2+ currents and shifted the I-V curves toward more negative potentials. These results suggest that the majority of Ca2+ channels in OHCs have L-type characteristics. The effects of ATP on Ca2+ channels of OHCs were heterogenous. ATP (100 microM) decreased Ca2+ channel currents by 31.7 +/- 5.6% at 0 mV and shifted Ca2+ tail activation curves toward more depolarized potentials in some cells (N = 6). By contrast, in others, ATP enhanced the currents by 43.5 +/- 12.5% at +10 mV (N = 6). In the presence of BayK, however, ATP-induced inhibition or enhancement of Ca2+ channel currents was attenuated. In addition, 100 microM ATP produced little effect on Ca2+ channel currents in another subpopulation of cells (N = 12). This heterogenous neuromodulation of Ca2+ channel currents by ATP may reflect a functional diversity among OHCs.
采用全细胞膜片钳技术研究了急性分离的豚鼠外毛细胞（OHC）中Ca2+通道电流及其被三磷酸腺苷（ATP）的调制情况。OHC的电流-电压（I-V）关系表明，Ca2+通道在-30 mV附近开放，在20 mM Ca2+和Ba2+的细胞外溶液中，电流分别在+10 mV和0 mV时达到最大值。BayK 8644（BayK，2 μM）使Ca2+峰值电流增加了3.5倍，并使I-V曲线向更负的电位移动。这些结果表明，OHC中的大多数Ca2+通道具有L型特征。ATP对OHC中Ca2+通道的影响是异质性的。ATP（100 μM）在0 mV时使Ca2+通道电流降低了31.7±5.6%，并使一些细胞（N = 6）的Ca2+尾电流激活曲线向更去极化的电位移动。相比之下，在其他细胞中，ATP在+10 mV时使电流增加了43.5±12.5%（N = 6）。然而，在存在BayK的情况下，ATP诱导的Ca2+通道电流抑制或增强作用减弱。此外，100 μM ATP对另一亚群细胞（N = 12）的Ca2+通道电流几乎没有影响。ATP对Ca2+通道电流的这种异质性神经调制可能反映了OHC之间的功能多样性。
