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 μmol·1-1 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 μmol·1-1 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 μmol·1-1 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 μmol·1-1 Cd2+ decreased the peak values of 50 mmol·1-1 K+ depolarization-induced [Ca2+]i transients to 30.4 ± 1.4% while 200 μmol·1-1 Cd2+ caused a drop to 2.5 ± 0.2%. 200 μmol·1-1 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.
|Number of pages||12|
|Journal||General physiology and biophysics|
|Publication status||Published - dec. 1 2001|
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