The ion channel properties of a rat recombinant neuronal nicotinic receptor are dependent on the host cell type

Abstract

1 A stable mammalian cell line (L‐α3β4) has been established which expresses the cloned rat neuronal nicotinic acetylcholine receptor (nAChR) subunits α3 and β4, which are the most abundant in autonomic ganglia. Ion channel properties of nAChRs expressed in L‐α3β4 cells were investigated by single‐channel and whole‐cell recording techniques, and compared with both rat α3β4 nAChRs expressed in Xenopus oocytes, and endogenous nicotinic receptors in rat superior cervical ganglion (SCO) neurones, using identical solutions for all cell types. 2 Acetylcholine (ACh) caused activation of single ion channel currents with a range of amplitudes. Some channels had high conductances (30–40 pS), and relatively brief lifetimes; these resembled the predominant native channel from SCG. Other channels had low conductances (20–26 pS) and long bursts of openings which were quite unlike native channels, but which were similar to channels formed by α3β4 in oocytes. Both types often occurred in the same patch. 3 Cytisine was about 3 times more potent than ACh (low‐concentration potency ratio) in L‐α3β4 cells, which is not dissimilar to the 5‐fold potency ratio found in both SCG and oocytes, whereas 1,1‐dimethyl‐4‐phenylpiperazinium (DMPP) was less potent than ACh in some cells (as in the oocyte), but more potent in others (as in SCG). 4 While the channels expressed in L‐α3β4 cells do not mimic exactly those expressed in rat SCG, they differ considerably from the same subunit combination expressed in oocytes. Larger conductance, SCG‐like channels were detected frequently in L‐α3β4, but were rarely, if ever, seen in oocytes injected with α3 and β4 mRNA. Our results indicate that ion channel properties such as single‐channel conductance can be influenced by the choice of heterologous expression system.