Estrogen transiently increases delayed rectifier, voltage-dependent potassium currents in ovine gonadotropes

Area of Science:

• Endocrinology
• Neuroendocrinology
• Cellular Electrophysiology

Background:

• Estrogen (E) modulates gonadotrope cell responsiveness to gonadotropin-releasing hormone (GnRH).
• GnRH stimulation alters pituitary cell electrophysiology, leading to hyperpolarization and increased action potential frequency after E treatment.
• The precise role of ion currents, particularly potassium (K+) currents, in mediating these E-induced changes remains to be fully elucidated.

Purpose of the Study:

• To investigate the role of K+ current in the altered electrophysiological response of gonadotropes to GnRH following estrogen treatment.
• To quantify the effect of E on K+ current density in enriched ovine gonadotrope cultures.

Main Methods:

• Primary cultures of ovine pituitary cells enriched for gonadotropes were utilized.
• Nystatin-perforated whole-cell patch-clamp recordings in voltage-clamp mode were employed to measure K+ current density.
• Cells were treated with varying doses and durations of E, and K+ current was measured before and after treatment.

Main Results:

• Estrogen treatment significantly increased unit K+ current density by approximately 180% compared to vehicle-treated cells after 16-20 hours.
• The effect of E on K+ current was dose- and time-dependent, with maximal effects observed at 16-20 hours.
• The time course of E-induced K+ current increase mirrored the time course of E's effect on luteinizing hormone (LH) release.

Conclusions:

• Estrogen significantly enhances K+ current in gonadotropes, primarily through voltage-dependent, delayed rectifier K+ channels (IK).
• The observed increase in K+ current is a key mechanism by which estrogen facilitates the GnRH-stimulated LH surge, which triggers ovulation.
• These findings provide critical insights into the electrophysiological basis of estrogen's regulatory role in the reproductive axis.