[Effects of free radicals and amyloid beta protein on the currents of expressed rat receptors in Xenopus oocytes].

AIM

To investigate the effects of free radicals (FRs) and amyloid beta protein (A beta 1-40) on the functions of expressed neurotransmitter receptors (NRs) from rat brains in Xenopus oocytes.

METHODS

Total RNA and Messenger RNA (mRNA) was prepared from 3-month-old Wistar rat brain tissues with Promega kits and microinjected into mature Xenopus oocytes (stage V - VI) with 50 nl (50 ng) for each oocyte for receptor expression and their currents were recorded with double electrode voltage clamp technique. Superoxide anion free radicals (SAFRs) and A beta 1-40 was added 12 h, 24 h, 96 h to incubation solution before recording.

RESULTS

The results showed that oocytes expressed mACh, glutamate, dopamine, serotonin and gamma-aminobutyric acid receptors. The current characteristics of these receptors were inward currents carried by chloride ion with their equilibrium potentials close to - 22 mV. A beta 1-40 and free radicals had a kind of inhibitory effect on the expressed GluR. When treated with 60 nmol/L A beta 1-40 over 24 h, the currents of GluR significantly decreased (25% off, P < :0.01). When oocytes were co-treated with 60 nmol/L A beta 1-40 and SAFRs over a period of 12 h, the currents of glutamate receptor significantly decreased (21% of P < 0.05), and the decreased percentage reached 52% over 24h co-treated with 60 nmol/L A beta 1-40 and SAFRs. Vitamin E had partial antagonistic effect against these effects.

CONCLUSION

The result suggests that A beta has a kind of inhibitory effects upon glutamate receptor, which is similar to those of free radicals. Their effects can be antagonized by vitamin E. This implies that A beta may play roles via inhibiting receptor function in pathophysiology of Alzheimer's disease.