Ca2+ channels that activate Ca2+-dependent K+ currents in neostriatal neurons.
It is demonstrated that not all voltage-gated calcium channel types expressed in neostriatal projection neurons (L, N, P, Q and R) contribute equally to the activation of calcium-dependent potassium currents. Previous work made clear that different calcium channel types contribute with a similar amount of current to whole-cell calcium current in neostriatal neurons. It has also been shown that spiny neurons possess both "big" and "small" types of calcium-dependent potassium currents and that activation of such currents relies on calcium entry through voltage-gated calcium channels. In the present work it was investigated whether all calcium channel types equally activate calcium-dependent potassium currents. Thus, the action of organic calcium channel antagonists was investigated on the calcium-activated outward current. Transient potassium currents were reduced by 4-aminopyridine and sodium currents were blocked by tetrodotoxin. It was found that neither 30 nM omega-Agatoxin-TK, a blocker of P-type channels, nor 200 nM calciseptine or 5 microM nitrendipine, blockers of L-type channels, were able to significantly reduce the outward current. In contrast, 400 nM omega-Agatoxin-TK, which at this concentration is able to block Q-type channels, and 1 microM omega-Conotoxin GVIA, a blocker of N-type channels, both reduced outward current by about 50%. These antagonists given together, or 500 nM omega-Conotoxin MVIIC, a blocker of N- and P/Q-type channels, reduced outward current by 70%. In addition, the N- and P/Q-type channel blockers preferentially reduce the afterhyperpolarization recorded intracellularly. The results show that calcium-dependent potassium channels in neostriatal neurons are preferentially activated by calcium entry through N- and Q-type channels in these conditions.
Vilchis
C
C
Instituto de Fisiología Celular, UNAM, México City, DF, México.
Bargas
J
J
Ayala
G X
GX
Galván
E
E
Galarraga
E
E
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D017072:Neostriatum / Q000166:cytology / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011188:Potassium; D002118:Calcium