Nonselective cation channel activated by patch excision from lobster olfactory receptor neurons. 
A nonselective cation channel activated by patch excision was characterized in inside-out patches from spiny lobster olfactory receptor neurons.  The channel, which was permeable to Na+, K+ and Cs+, had a conductance of 320 pS and was weakly voltage dependent in the presence of micromolar divalent cations.  Millimolar internal divalent cations caused a voltage- and concentration-dependent block of Na+ permeation.  Analysis of the voltage dependence indicated that the proportion of the membrane's electric field sensed by Mg2+ was greater than 1, suggesting that the channel contains a multi-ion pore.  Internal divalent cations also reduced the frequency of channel opening in a concentration-dependent, but not voltage-dependent, manner, indicating that different cation binding sites affect gating and conductance.  While block of gating prevented determining if internal divalent cations permeate the channel, a channel highly permeable to external divalent cations was observed upon patch excision to the inside-out configuration.  The monovalent and divalent cation conductances shared activation by patch excision, weak voltage dependence, and steady-state activity, suggesting that they are the same channel.  These data extend our understanding of this type of channel by demonstrating permeation by monovalent cations, detailing Mg2+ block of Na+ permeation, and demonstrating the channel's presence in arthropods.