1. A comparative study of the whole‐cell and single‐channel properties of cloned and native mouse 5‐hydroxytryptamine ionotropic receptors (5‐HT3) was undertaken using mammalian cell lines expressing the cloned 5‐HT3 receptor subunit A (5‐HT3R‐A), superior cervical ganglia (SCG) neurones and N1E‐115 cells. 2. No pharmacological difference was found in the sensitivity to the agonists 5‐HT and 2‐methyl‐5‐HT, or to the antagonists d‐tubocurare and 3‐tropanyl‐3,5‐dichlorobenzoate (MDL‐72222). 3. Current‐voltage (I‐V) relationships of whole‐cell currents showed inward rectification in the three preparations. Rectification was stronger both in cells expressing the 5‐HT3R‐A subunit and in N1E‐115 cells when compared with SCG neurones. 4. No clear openings could be resolved in 5‐HT‐activated currents in patches excised from cells expressing the 5‐HT3R‐A subunit or N1E‐115 cells. Current fluctuation analysis of whole‐cell and excised‐patch records revealed a slope conductance of 0.4‐0.6 pS in both preparations. Current‐voltage relationships of these channels showed strong rectification that fully accounted for the whole‐cell voltage dependence. 5. In contrast, single channels of about 10 pS were activated by 5‐HT in patches excised from SCG neurones. The weak voltage dependence of their conductance did not account completely for the rectification of whole‐cell currents. A lower unitary conductance (3.4 pS) was inferred from whole‐cell noise analysis. 6. We conclude that the receptor expressed from the cloned cDNA is indistinguishable from the 5‐HT3 receptor of N1E‐115 cells, suggesting an identical structure for these two receptors. The higher conductance and different voltage dependence of the 5‐HT3 receptor in SCG neurones might indicate the participation of an additional subunit in the structure of native ganglionic 5‐HT3 receptors. Homo‐oligomeric 5‐HT3R‐A channels may also be present as suggested by the lower conductance estimated by whole‐cell noise analysis.
The Journal of Physiology – Wiley
Published: Dec 1, 1994
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