A cDNA coding for the human neuronal nicotinic α7 receptor subunit with Leu-248 mutated to threonine was expressed in Xenopus oocytes. When activated by acetylcholine (AcCho), the receptors expressed generated currents that had low desensitization, linear current-voltage relation, and high apparent affinity for both AcCho and nicotine. These characteristics are similar to those already described for the chick threonine-for-leucine-247 ↓ nicotinic AcCho receptor (nAcChoR) mutant (L247Tα7). These properties were all substantially maintained when the human L248Tα7 mutant was transiently expressed in human Bosc 23 cells. Simultaneous whole-cell clamp and fluorescence measurements with the Ca2+ indicator dye Fura-2 showed that nicotine induced a Ca2+ influx in standard 2 mM Ca2+ solution. The average fractional Ca2+ current flowing through L248Tα7 nAcChoRs was 6.7%, which is larger than that flowing through muscle αβεδ nAcChoRs (4.1%). The relative Ca2+ permeability, determined in oocytes in the absence of Cl-, was measured from the shift in reversal potential caused by increasing the external Ca2+ concentration from 1 to 10 mM. The human wild-type α7 nAcChoR was found to be more permeable than the L248Tα7 mutant to Ca2+. Our findings indicate that the Ca2+ permeability of the homomeric α7 nAcChoR is larger than that of the heteromeric neuronal nicotinic receptors studied to date and is possibly similar to that of the N-methyl-D-aspartate subtype of brain glutamate receptors.
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - Mar 28 2000|
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