Slow nonselective cation conductances play a central role in determining the excitability of many neurons, but heretofore this channel type has not been analyzed at the single-channel level. Neurotensin (NT) excites cultured dopaminergic neurons from the ventral tegmental area primarily by increasing such a cation conductance. Using the outside-out configuration of the patch clamp, we elicited single-channel activity of this NT-induced cation channel. Channel activity was blocked by the nonpeptide NT antagonist SR48692, indicating that the response was mediated by NT receptors. The channel opened in both solitary form and in bursts. The reversal potential was -4.2 +/- 1.7 mV, and the elementary conductance was 31 pS at -67 mV with [Na+]o = 140 mM, [Cs+]o = 5 mM, [Na+]i = 88 mM, and [Cs+]i = 74 mM. Thus, the channel was permeable to both Na+ and Cs+. From these characteristics, it is likely that this channel is responsible for the whole-cell current we studied previously. In guanosine 5'-[gamma-thio]triphosphate-loaded cells, NT irreversibly activated about half of the channel activity, suggesting that at least part of the response was mediated by a G protein. Similar channel activity could be induced occasionally in the cell-attached configuration by applying NT outside the patch region.