Voltage-dependent Ca2+ channels in spiral ganglion cells (SGCs) isolated from guinea pig cochlea were investigated using the patch-clamp technique in a whole-cell recording mode. The voltage-dependent Na+ and K+ currents were blocked by adding tetrodotoxin, 4-aminopyridine, and tetraethylammonium to the external solution and by using choline or Cs+ in the external and internal solutions instead of Na+ or K+, respectively. The depolarizing voltage steps evoked inward currents with slow current decay. The maximum amplitude of the inward current increased in a hyperbolic manner with increasing extracellular Ca2+ concentration, indicating that the inward current was a voltage-dependent Ca2+ current (ICa). In 5 mM Ca2+ external solution, the ICa activated from a membrane potential around -60 mV and reached full activation at about -10 mV. The ICa inactivated from about -60 mV and became fully inactivated at about 0 mV, consistent with the high-voltage-activated Ca2+ channel subtype. Ionic selectivities for Ca2+ channels in SGCs were as follows: Ca2+>Ba2+>Sr2+. Effects of both inorganic and inorganic Ca2+ antagonists also were examined. The inhibitory strength was as follows: La3+>Cd2+>Ni2+≥Co2+ for inorganic Ca2+ antagonists, and flunarizine>nicardipine>methoxyverapamil >dilitiazem for organic ones.
All Science Journal Classification (ASJC) codes
- Sensory Systems