Effects of divalent cations on voltage-gated Ca2+ channels and depolarization-induced [Ca2+], transients of freshly isolated pyramidal cells of the rat dorsal cochlear nucleus.
The effects of divalent cations on voltage-activated Ca2+ channels and depolarization-evoked cytoplasmic [Ca2+] elevations were studied in pyramidal neurones isolated from the dorsal cochlear nucleus of the rat. Ca2+ currents were recorded using the whole-cell configuration of the patch-clamp technique. 10 micromol x l(-1) Cd2+ exerted a greater blocking effect on the high-voltage activated (HVA) currents than on the low-voltage activated (LVA) ones (decrease to 26.6+/-2.5% and to 87.8+/-2.1%, respectively). The blocking effect of 200 micromol x l(-1) Cd2+ was more pronounced and the difference between the effect on the HVA and LVA currents became smaller (decrease to 11.7+/-2.1% and to 32.4+/-2.7%, respectively). 200 micromol x l(-1) Ni2+ reduced the LVA component more effectively (to 77.6+/-5.4%) than the HVA one (to 86.9+/-2.6%). Cytoplasmic [Ca2+] changes were measured applying a fluorimetric technique (Fura-2). 10 micromol x l(-1) Cd2+ decreased the peak values of 50 mmol x l(-1) K+ depolarization-induced [Ca2]+i transients to 30.4+/-1.4% while 200 micromol x l(-1) Cd2+ caused a drop to 2.5+/-0.2%. 200 micromol x l(-1) Ni2+ decreased the peak of the transients to 69.6+/-2.9%. Comparison of the blocking effects of divalent cations on Ca2+ currents and [Ca2+]i transients supports further the conclusion that the depolarization-induced [Ca2+]i changes are produced mainly by the activation of the HVA Ca2+ channels.
Harasztosi
C
C
Department of Physiology, University of Debrecen, Medical and Health Science Centre, Medical School, Hungary.
Rusznák
Z
Z
Kovács
L
L
Szücs
G
G
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry*; D002412:Cations; D017626:Cochlear Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004594:Electrophysiology; D011188:Potassium / Q000378:metabolism; D017966:Pyramidal Cells / Q000378:metabolism*; D051381:Rats; D013997:Time Factors
D015220:Calcium Channels; D002412:Cations; D011188:Potassium; D002118:Calcium