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Ca 2+ ‐dependent regulation of a non‐selective cation channel from Aplysia bag cell neurones
Author(s) -
Lupinsky Derek A.,
Magoski Neil S.
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2006.105833
Subject(s) - calmodulin , aplysia , biophysics , extracellular , chemistry , cytoplasm , membrane potential , electrophysiology , biochemistry , biology , neuroscience , enzyme
Ca 2+ ‐activated, non‐selective cation channels feature prominently in the regulation of neuronal excitability, yet the mechanism of their Ca 2+ activation is poorly defined. In the bag cell neurones of Aplysia californica , opening of a voltage‐gated, non‐selective cation channel initiates a long‐lasting afterdischarge that induces egg‐laying behaviour. The present study used single‐channel recording to investigate Ca 2+ activation in this cation channel. Perfusion of Ca 2+ onto the cytoplasmic face of channels in excised, inside‐out patches yielded a Ca 2+ activation EC 50 of 10 μ m with a Hill coefficient of 0.66. Increasing Ca 2+ from 100 n m to 10 μ m caused an apparent hyperpolarizing shift in the open probability ( P o ) versus voltage curve. Beyond 10 μ m Ca 2+ , additional changes in voltage dependence were not evident. Perfusion of Ba 2+ onto the cytoplasmic face did not alter P o ; moreover, in outside‐out recordings, P o was decreased by replacing external Ca 2+ with Ba 2+ as a charge carrier, suggesting Ca 2+ influx through the channel may provide positive feedback. The lack of Ba 2+ sensitivity implicated calmodulin in Ca 2+ activation. Consistent with this, the application to the cytoplasmic face of calmodulin antagonists, calmidazolium and calmodulin‐binding domain, reduced P o , whereas exogenous calmodulin increased P o . Overall, the data indicated that the cation channel is activated by Ca 2+ through closely associated calmodulin. Bag cell neurone intracellular Ca 2+ rises markedly at the onset of the afterdischarge, which would enhance channel opening and promote bursting to elicit reproduction. Cation channels are essential to nervous system function in many organisms, and closely associated calmodulin may represent a widespread mechanism for their Ca 2+ sensitivity.