Calcium signaling in single rat Leydig cells

Area of Science:

• Endocrinology
• Cell Biology
• Reproductive Physiology

Background:

• Leydig cell steroidogenesis is regulated by hormones activating adenylate cyclase or phospholipase C.
• Luteinizing hormone (LH) controls androgen production via cAMP, but Ca2+-mobilizing stimuli's role is less defined.
• Adult rat Leydig cells lack voltage-sensitive calcium channels and do not respond to LH, CRF, or serotonin with increased intracellular calcium ([Ca2+]i).

Purpose of the Study:

• To investigate the role of calcium signaling in Leydig cell function.
• To identify specific hormones that mobilize intracellular calcium in Leydig cells.
• To characterize the nature and cellular distribution of calcium responses induced by GnRH and ET-1.

Main Methods:

• Measurement of intracellular calcium ([Ca2+]i) in adult rat Leydig cells using fura-2 fluorescence.
• Stimulation of Leydig cells with various agents including high K+, Bay K 8644, LH, CRF, serotonin, GnRH, and endothelin-1 (ET-1).
• Use of specific receptor antagonists ([Dp-Glu1,D-Phe2,D-Trp3,6]GnRH for GnRH and BQ-123 for ET-1) to block calcium responses.

Main Results:

• GnRH and ET-1 induced rapid, transient [Ca2+]i elevations in a subpopulation (approx. 30%) of Leydig cells, independent of extracellular calcium.
• These responses were blocked by specific GnRH and ETA receptor antagonists, respectively.
• GnRH primarily affected medium-sized Leydig cells, while ET-1 predominantly acted on large Leydig cells, with some cells expressing both receptors.

Conclusions:

• Single Leydig cells exhibit all-or-none, monophasic [Ca2+]i responses to GnRH and ET-1 via their specific receptors.
• This transient calcium signaling pathway may regulate short-term Leydig cell functions.
• Calcium signaling could potentially modulate the cAMP-mediated actions of gonadotropins in Leydig cells.