Actions of pentobarbital on rat brain receptors expressed in Xenopus oocytes

Abstract

Functional receptor channels activated by GABA and other neurotransmitters were “transplanted” from rat brain to Xenopus oocytes by injecting the oocytes with total poly(A)+ mRNA isolated from rat or chick brain. Membrane currents elicited in the oocyte by GABA inverted polarity at about the chloride equilibrium potential (ca. -25 mV). Pentobarbital potentiated the GABA-activated currents, without appreciably changing the reversal potential or form of the current- voltage relationship. At low (less than 10(-5) M) concentrations of GABA, pentobarbital (100 microM) potentiated the responses by a factor of 10 or more, but responses to high (ca. 1 mM) concentrations of GABA were almost unchanged. Half-maximal activation of the response was obtained with about 3 X 10(-5) M GABA when applied alone and with about 4 X 10(-6) M GABA when applied together with 100 microM pentobarbital. At low doses of GABA, the size of the current increased as the 1.4th power of GABA concentration, but this relationship became nearly linear in the presence of pentobarbital. The potentiation of the GABA response increased linearly with concentrations of pentobarbital up to about 300 microM, reaching a maximum of about 50-fold. At higher concentrations of pentobarbital, the response to GABA declined. Relaxations of GABA- activated currents following voltage steps became slower in the presence of pentobarbital, suggesting that the open life-time of the channels was prolonged. In addition to actions on GABA-activated currents, pentobarbital itself elicited a small membrane current that inverted polarity at a potential (-10 mV) more positive than the GABA- activated current.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonistic action of pitrazepin on human and rat GABAA receptors

“…The Hill coe cients were 1.5 for both rat cortex and a 1 b 2 g 2S receptors, whereas a 1 b 2 receptors gave a Hill coe cient of 1.1. These values are similar to those previously reported for oocytes injected with mRNA from rat cerebral cortex (Parker et al, 1986;Polenzani et al, 1991) and oocytes expressing rat GABA A receptors containing a 1 b 2 or a 1 b 2 g 2S subunits (Sigel et al, 1990).…”

“…The positive allosteric modulator pentobarbitone (30 mM) potentiated the GABA-currents (c.f. Gundersen et al, 1984;Parker et al, 1986) elicited by all three types of receptors, but its e cacy depended on the receptor subunit composition. In respect to the control (GABA-alone) the potentiation was: rat cortex, 424+45%, n=5, a 1 b 2 g 2S , 345+14%, n=6, and a 1 b 2 , 197+35%, n=5.…”

Expression of human epileptic temporal lobe neurotransmitter receptors inXenopusoocytes: An innovative approach to study epilepsy

“…1C). The latter value was considerably larger than many EC 50 values reported in the literature (11)(12)(13)(14)(15)(16)(17), but similar to the EC 50 found with TL ganglioglioma mRNA (patient 9, Table 1; not shown).…”

Barbiturate interactions at the human GABAA receptor: dependence on receptor subunit combination

“…As a6 is located primarily on cerebellar granule cells (Baude et al, 1992;Hadingham et al, 1995 unpublished observations), this cell type may show a similar profile to that observed here. GABAA receptors from whole rat or chick brain mRNA expressed in Xenopus oocytes, showed robust potentiation and small direct activation by pentobarbitone (Parker et al, 1986). Previous results with recombinant GABAA receptors have demonstrated both potentiation and direct activation of receptors by pentobarbitone (Sigel et al, 1990).…”