Effects of defolliculation on membrane current responses of Xenopus oocytes.

Effects of defolliculation on membrane current responses of Xenopus oocytes. 1. Catecholamines, adenosine, gonadotrophins, vasoactive intestinal peptide (VIP) and E‐series prostaglandins all elicit K+ currents in follicle‐enclosed Xenopus oocytes. Evidence suggests that cyclic nucleotides act as intracellular messengers in the activation of this K+ conductance. Muscarinic agonists and some divalent cations (e.g. Co2+, Mn2+, Ni2+ and Cd2+) elicit slow oscillatory Cl‐ currents, which are activated through hydrolysis of inositol phospholipids and mobilization of intracellular calcium by inositol phosphates. 2. We investigated whether these membrane current responses were generated in the oocyte itself or in enveloping follicular cells which are coupled to the oocyte by gap junctions. Oocytes were defolliculated, either enzymatically using collagenase, or by manual dissection combined with rolling over poly‐L‐lysine‐coated slides. Removal of follicular cells was checked using scanning electron microscopy. Membrane current responses of defolliculated oocytes were compared with responses seen in follicle‐enclosed oocytes taken from the same ovary. 3. The K+ responses evoked by all the various hormones/neurotransmitters were either drastically reduced (greater than 90%) or abolished by defolliculation. K+ currents generated by the adenylate cyclase activator forskolin and by intraoocyte injection of adenosine 3',5'‐cyclic monophosphate (cyclic AMP), or guanosine 3',5'‐cyclic monophosphate were similarly reduced in defolliculated oocytes. In contrast, oscillatory Cl‐ currents to acetylcholine and divalent cations were selectively preserved through defolliculation. 4. Injection of cyclic AMP (1‐20 pmol) into defolliculated oocytes had little or no effect on oscillatory Cl‐ currents elicited by ACh. However, the calcium‐dependent transient Cl‐ current, activated by depolarization of the oocyte membrane, was consistently potentiated (100‐900%) by injections of cyclic AMP (1‐10 pmol). 5. These experiments suggest that cyclic nucleotide‐activated K+ currents arise essentially in follicular cells and are monitored within the oocyte through electrical coupling by gap junctions. Oscillatory Cl‐ responses evoked by ACh and divalent cations are produced largely or wholly in the oocyte itself. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Physiology Wiley

Effects of defolliculation on membrane current responses of Xenopus oocytes.

The Journal of Physiology, Volume 416 (1) – Sep 1, 1989

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Publisher
Wiley
Copyright
© 2014 The Physiological Society
ISSN
0022-3751
eISSN
1469-7793
DOI
10.1113/jphysiol.1989.sp017780
Publisher site
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Abstract

1. Catecholamines, adenosine, gonadotrophins, vasoactive intestinal peptide (VIP) and E‐series prostaglandins all elicit K+ currents in follicle‐enclosed Xenopus oocytes. Evidence suggests that cyclic nucleotides act as intracellular messengers in the activation of this K+ conductance. Muscarinic agonists and some divalent cations (e.g. Co2+, Mn2+, Ni2+ and Cd2+) elicit slow oscillatory Cl‐ currents, which are activated through hydrolysis of inositol phospholipids and mobilization of intracellular calcium by inositol phosphates. 2. We investigated whether these membrane current responses were generated in the oocyte itself or in enveloping follicular cells which are coupled to the oocyte by gap junctions. Oocytes were defolliculated, either enzymatically using collagenase, or by manual dissection combined with rolling over poly‐L‐lysine‐coated slides. Removal of follicular cells was checked using scanning electron microscopy. Membrane current responses of defolliculated oocytes were compared with responses seen in follicle‐enclosed oocytes taken from the same ovary. 3. The K+ responses evoked by all the various hormones/neurotransmitters were either drastically reduced (greater than 90%) or abolished by defolliculation. K+ currents generated by the adenylate cyclase activator forskolin and by intraoocyte injection of adenosine 3',5'‐cyclic monophosphate (cyclic AMP), or guanosine 3',5'‐cyclic monophosphate were similarly reduced in defolliculated oocytes. In contrast, oscillatory Cl‐ currents to acetylcholine and divalent cations were selectively preserved through defolliculation. 4. Injection of cyclic AMP (1‐20 pmol) into defolliculated oocytes had little or no effect on oscillatory Cl‐ currents elicited by ACh. However, the calcium‐dependent transient Cl‐ current, activated by depolarization of the oocyte membrane, was consistently potentiated (100‐900%) by injections of cyclic AMP (1‐10 pmol). 5. These experiments suggest that cyclic nucleotide‐activated K+ currents arise essentially in follicular cells and are monitored within the oocyte through electrical coupling by gap junctions. Oscillatory Cl‐ responses evoked by ACh and divalent cations are produced largely or wholly in the oocyte itself.

Journal

The Journal of PhysiologyWiley

Published: Sep 1, 1989

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