Cholinergic and catecholaminergic receptors in the Xenopus oocyte membrane

Abstract

SUMMARY1. Neurotransmitter-receptors in the membrane of Xenopus oocytes have been studied using electrophysiological techniques. Neurotransmitters and related agents were applied while recording either membrane potential or membrane current. The majority of ovarian oocytes used were at stages IV and V.2. Three types of oocytes were examined: inner ovarian epithelium covered (e.c.) oocytes; epithelium manually removed (e.r.) oocytes; and collagenase treated (c.t.) ooctyes.3. Ovarian oocytes are sensitive to some cholinergic and catecholaminergic agents. Responses to serotonin were seldom observed and when present were much weaker than responses to other agents. No responses were observed to the amino acids: aspartate, glutamate, y-aminobutyric acid, and glycine; or to octopamine and histamine.4. Acetylcholine (ACh) usually depolarized the membrane, in a dose-dependent manner, with threshold concentrations as low as 10-9 M. The ACh-potential was due to an increase in Cl permeability and had a reversal potential around -19 mV. The intracellular Cl ion activity, measured with a Cl-ion sensitive micro-electrode, was about 65 mm and the estimated Cl-ion equilibrium potential, EC1, agreed with the reversal potential of the ACh-potential.5. Curare (10-4 M), tetrodotoxin (10-6 M), or ac-bungarotoxin (10-6 g/ml.) did not block the response to 10-6 M-ACh; whereas atropine (10-7 M) blocked it. No response to nicotinic agents (e.g. nicotine, 1,1-dimethyl-4-phenylpiperazinium) was observed. These results suggest that the ACh receptors in the oocyte membrane are muscarinic in nature.6. The apparent latency ofthe ACh potential, examined by ionophoretic application of ACh to e.r. oocytes and c.t. oocytes, ranged from 0 5 see to over 20 sec. Intracellular injection of ACh was without effect.7. Responses to catecholamines were observed mostly in e.c. oocytes; while in e.r. and c.t. oocytes they were rare and of very small amplitudes.

Antagonistic action of pitrazepin on human and rat GABAA receptors

“…These receptors display properties very similar to those of native receptors present in the vertebrate central nervous system. Such properties include the doseresponse relationship (Tyndale et al, 1995), the timedependent inactivation (Poulter et al, 1996) and a reversal potential similar to the chloride equilibrium potential (Kusano et al, 1982;Miledi et al, 1982). The EC 50 values obtained here for rat cerebral cortex and for a 1 b 2 or a 1 b 2 g 2S human GABA A receptors are consistent with those found in previous studies, demonstrating that functional GABA A -receptors are formed also in the absence of the g 2 -subunit (McKernan and Whiting, 1996).…”

Gating of IsK expressed in Xenopus oocytes depends on the amount of mRNA injected.

“…Currents were recorded with a conventional two-electrode voltage clamp (Dagan, Minneapolis, MN) (Kusano, Miledi, and Stinnakre, 1982). Intracellular glass microelectrodes were filled with 3 M KC1 and had tip resistances between 0.5 and 3 MI~.…”

Inositol phospholipid metabolism in Xenopus oocytes mediated by endogenous Go and Gi proteins

“…These responses involve the signal transduction from the activated receptor to G-protein and PLC, the production of inositol 1,4,5-trisphosphate (IP,), intercellular Ca*' mobilization, and the opening of chloride channels. It has been shown that, under some conditions, native oocytes have endogenous muscarinic receptors which produce ACh-stimulated chloride current responses [20]. However, under our conditions, oocytes without mRNA-injection rarely produced such responses to ACh, and we could assume that ACh-evoked current responses were due to exogenously induced Ml receptors.…”