Voltage-dependent Ca2+ channels in the spiral ganglion cells of guinea pig cochlea.
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 O 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 organic Ca2+ antagonists also were examined. The inhibitory strength was as follows: La3+ > Cd2+ > Ni2+ > or = Co2+ for inorganic Ca2+ antagonists, and flunarizine > nicardipine > methoxyverapamil > diltiazem for organic ones.
Hisashi
K
K
Department of Otorhinolaryngology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Nakagawa
T
T
Yasuda
T
T
Kimitsuki
T
T
Komune
S
S
Komiyama
S
S
D015761:4-Aminopyridine / Q000633:toxicity; D000818:Animals; D002121:Calcium Channel Blockers / Q000633:toxicity; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002586:Cesium / Q000737:chemistry / Q000378:metabolism; D002794:Choline / Q000737:chemistry / Q000378:metabolism; D003051:Cochlea / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects; D008670:Metals / Q000633:toxicity; D018408:Patch-Clamp Techniques; D012015:Reference Standards; D013136:Spiral Ganglion / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000633:toxicity; D013779:Tetrodotoxin / Q000633:toxicity
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008670:Metals; D013757:Tetraethylammonium Compounds; D002586:Cesium; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D002794:Choline