Influence of Ca2+-binding proteins and the cytoskeleton on Ca2+-dependent inactivation of high-voltage activated Ca2+ currents in thalamocortical relay neurons.
Ca2+-dependent inactivation (CDI) of high-voltage activated (HVA) Ca2+ channels was investigated in acutely isolated and identified thalamocortical relay neurons of the dorsal lateral geniculate nucleus (dLGN) by combining electrophysiological and immunological techniques. The influence of Ca2+-binding proteins, calmodulin and the cytoskeleton on CDI was monitored using double-pulse protocols (a constant post-pulse applied shortly after the end of conditioning pre-pulses of increasing magnitude). Under control conditions the degree of inactivation (34+/-9%) revealed a U-shaped and a sigmoid dependency of the post-pulse current amplitude on pre-pulse voltage and charge influx, respectively. In contrast to a high concentration (5.5 mM) of EGTA (31+/-3%), a low concentration (3 microM) of parvalbumin (20+/-2%) and calbindin(D28K) (24+/-4%) significantly reduced CDI. Subtype-specific Ca2+ channel blockers indicated that L-type, but not N-type Ca2+ channels are governed by CDI and modulated by Ca2+-binding proteins. These results point to the possibility that activity-dependent changes in the intracellular Ca2+-binding capacity can influence CDI substantially. Furthermore, calmodulin antagonists (phenoxybenzamine, 22+/-2%; calmodulin binding domain, 17+/-1%) and cytoskeleton stabilizers (taxol, 23+/-5%; phalloidin, 15+/-3%) reduced CDI. Taken together, these findings indicate the concurrent occurrence of different CDI mechanisms in a specific neuronal cell type, thereby supporting an integrated model of this feedback mechanism and adding further to the elucidation of the role of HVA Ca2+ channels in thalamic physiology.
Meuth
Sven G
SG
Otto-von-Guericke Universität, Medizinische Fakultät, Institut für Physiologie, Leipziger Strasse 44, 39120, Magdeburg, Germany. sven.meuth@gmx.de
Kanyshkova
Tatjana
T
Landgraf
Peter
P
Pape
Hans-Christian
HC
Budde
Thomas
T
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology*; D003078:Colchicine / Q000494:pharmacology; D003572:Cytochalasins / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D005829:Geniculate Bodies / Q000166:cytology / Q000502:physiology*; D009434:Neural Pathways; D017239:Paclitaxel / Q000494:pharmacology; D010590:Phalloidine / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans
D000972:Antineoplastic Agents, Phytogenic; D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D003572:Cytochalasins; D010590:Phalloidine; D017239:Paclitaxel; D003078:Colchicine; D002118:Calcium