Expression and characteristics of nicotinic receptors in Xenopus oocytes

Torpedo electroplax nicotinic receptor (N₂-ChR) and rat brain nicotinic receptor (N₁-ChR) were synthesized in Xenopus oocytes after injection with mRNAs transcripted in vitro from plasmids pSP64T containing the four full length Torpedo N₂-ChR subunit cDNAs or purified from yeast transferred with rat brain N₁-ChR α₄ and β₂ subunit cDNAs. Membrane current in the injected oocytes was measured with voltage clamp technique by part cell flow and/or whole cell flow with various concentrations of carbamylcholine, the dose responses to carbamylcholine were similar. K₁ of 0.528 and 0.491 mmol · L^-1, Φ^-1 of 3.861 and 3.891 were obtained in oocytes injected with Torpedo N₂-ChR mRNA by whole cell flow and part cell flow, respectively. A dose-response curve shifted to left but similar to what is obtained from Torpedo N₂-ChR, a K₁ of 0.140 mmol · L^-1 and a Φ^-1 of 3.125 were obtained in the oocytes injected with rat brain N₁-ChR by whole cell flow.