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Xenopus oocyte K+ current. I. FSH and adenosine stimulate follicle cell-dependent currents. | LitMetric

AI Article Synopsis

  • The study focuses on the ovarian follicles of Xenopus laevis frogs, highlighting how adenosine activates K+ currents in these follicles through the influence of cAMP.
  • It was found that specific adenosine analogs and follicle-stimulating hormone (FSH) induce hyperpolarizing currents, linking their effects to the activation of adenylyl cyclase and the subsequent production of cAMP.
  • The research suggests that for effective hyperpolarization to occur in response to these stimuli, both the oocyte and follicle cells need to have active cAMP-dependent protein kinase, as demonstrated by the difference in responses between intact follicles and stripped oocytes.

Article Abstract

Ovarian follicles of Xenopus laevis frogs consist of a single large oocyte surrounded by follicle cells attached to the oocyte by gap junctions. Adenosine has been found to activate an outward K+ current in follicles. This response is reduced by microinjection of protein kinase inhibitor (PKI), suggesting that adenosine 3',5'-cyclic monophosphate (cAMP) mediates the response. To investigate this further, we verified previous studies that indicate that several methods of elevating cAMP in follicles activate hyperpolarizing outward currents. The potency of two adenosine analogues to hyperpolarize follicles, 5'-N-ethylcarboxamidoadenosine (NECA) greater than cyclopentyladenosine, is indicative of A2 receptors that are characteristically coupled to adenylyl cyclase. We also report for the first time that another stimulator of adenylyl cyclase, follicle-stimulating hormone (FSH), also induces a hyperpolarizing current in follicles which is carried by K+ and attenuated by injection of PKI. We used a novel procedure to completely remove follicle cells from oocytes. Intact follicles, but not oocytes completely stripped of follicle cells, hyperpolarized in response to FSH, NECA, dibutyryl cAMP, microinjected cAMP, and forskolin, but not to dideoxyforskolin (which does not activate adenylyl cyclase). Injection of the catalytic subunit of cAMP-dependent protein kinase (which is too large to traverse gap junctions) into oocytes of intact follicles failed to activate a K+ current. These data suggest that FSH and adenosine hyperpolarize follicles by stimulating adenylyl cyclase and that cAMP-dependent protein kinase must be activated on both sides of follicle cell-oocyte gap junctions to elicit a hyperpolarizing K+ current.

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Source
http://dx.doi.org/10.1152/ajpcell.1990.259.5.C775DOI Listing

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