Epithelium and/or theca are required for ATP-elicited K+ current in follicle-enclosed Xenopus oocytes.
The Xenopus follicular cell membrane is endowed with ATP-sensitive K+ channels, which are operated by various transmitters. These generate the ionic response named IK,cAMP via a mechanism that involves intracellular cAMP synthesis. It is known that opening these K+ channels favors oocyte maturation. Follicle stimulation by adenosine (Ado) or ATP consistently generates a strong IK,cAMP via activation of P1 and P3 purinergic receptors; however, ATP can also inhibit IK,cAMP, apparently acting on a third receptor type. Here, we show that IK,cAMP might be elicited by ATP released within the follicle, and that current activation by ATP was entirely dependent on the presence of epithelial and/or theca layers. Morphological studies confirmed that removal of epithelium/theca in these follicles (e.t.r.) was complete, and activation of fast Cl- (Fin) currents by ATP in e.t.r. follicles confirmed that communication between oocyte and follicular cells remained unchanged. Thus, dependence on epithelium/theca was specific for ATP-elicited K+ current. Using UTP and betagamma-MeATP as specific purinergic agents for IK,cAMP inhibition and activation, respectively, it was found that inhibition of IK,cAMP elicited by ATP or UTP was robustly present in e.t.r. follicles but was absent or strongly decreased in whole follicles (w.f.). Accordingly, this indicated that in w.f., epithelium and/or theca downregulated the IK,cAMP inhibition evoked by ATP, and that this control mechanism was absent in e.t.r. follicles. We suggest that this notable action on follicular cells involves one or both of two mechanisms, a paracrine transmitter released from epithelial and/or theca layers and action of ecto-ATPases.
Saldaña
Carlos
C
Laboratorio de Neurofisiología Celular, Departamento de Neurobiología Celular y Molecular, Instituto de Neurobiología UNAM, México.
Vázquez-Cuevas
Francisco
F
Garay
Edith
E
Arellano
Rogelio O
RO
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005260:Female; D005905:Glyburide / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006080:Ovarian Follicle / Q000033:anatomy & histology; D010095:Oxotremorine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D013799:Theca Cells / Q000166:cytology / Q000378:metabolism; D014982:Xenopus laevis
D000889:Anti-Arrhythmia Agents; D018721:Muscarinic Agonists; D015221:Potassium Channels; D010095:Oxotremorine; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D011188:Potassium; D005905:Glyburide