Sodium-activated cation channels in peptidergic nerve terminals.
The patch-clamp technique was utilized to characterize a cation channel in peptidergic nerve terminals isolated from a crustacean neurosecretory system. The cation channel exhibits the unique property of being activated by [Na+]. Distributions of open times demonstrate the presence of two open states with a shift of the distribution from predominantly short open times at [Na+] less than or equal to 10 mM to a predominantly long open state at [Na+] greater than or equal to 40 mM. Desensitization of channel activation occurs on prolonged exposure to [Na+] greater than 40 mM. Open probability increased steeply with [Na+] but was largely independent of membrane potential. Comparison of current-voltage relationships from single dissociated terminals and from those in the intact system show no differences in conductance or selectivity with nearly equal permeability to Na+ and K+, and impermeability to Cs+, divalent cations and anions. Flickering block occurred with [Ca2+]i greater than 1 microM. We propose that Na-activated cation (NAC) channels are activated by Na+ entering during action potentials and provide a sustained depolarizing current that can help sustain repetitive or bursting activity and subsequent facilitation of secretion from these nerve terminals.
Békésy Laboratory of Neurobiology, University of Hawaii, Honolulu 96822.
E L
EL
Stuenkel
P
P
Ruben
I M
IM
Cooke
J R
JR
Lemos
D000818:Animals; D003386:Brachyura / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009479:Neuropeptides / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*
D007473:Ion Channels; D009479:Neuropeptides; D012964:Sodium