Kisspeptin Depolarizes Gonadotropin-Releasing Hormone Neurons through Activation of TRPC-Like Cationic Channels

Abstract

Kisspeptin and its cognate receptor, GPR54, are critical for reproductive development and for the regulation of gonadotropin-releasing hormone (GnRH) secretion. Although kisspeptin has been found to depolarize GnRH neurons, the underlying ionic mechanism has not been elucidated. Presently, we found that kisspeptin depolarized GnRH neurons in a concentration-dependent manner with a maximum depolarization of 22.6 Ϯ 0.6 mV and EC 50 of 2.8 Ϯ 0.2 nM. Under voltage-clamp conditions, kisspeptin induced an inward current of 18.2 Ϯ 1.6 pA (V hold ϭ Ϫ60 mV) that reversed near Ϫ115 mV in GnRH neurons. The more negative reversal potential than E K ϩ (Ϫ90 mV) was caused by the concurrent inhibition of barium-sensitive, inwardly rectifying (Kir) potassium channels and activation of sodiumdependent, nonselective cationic channels (NSCCs). Indeed, reducing extracellular Na ϩ (to 5 mM) essentially eliminated the kisspeptininduced inward current. The current-voltage relationships of the kisspeptin-activated NSCC currents exhibited double rectification with negative slope conductance below Ϫ40 mV in the majority of the cells. Pharmacological examination showed that the kisspeptin-induced inward currents were blocked by TRPC (canonical transient receptor potential) channel blockers 2-APB (2-aminoethyl diphenylborinate), flufenamic acid, SKF96365 (1-[␤-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride), and Cd 2ϩ, but not by lanthanum (100 M). Furthermore, single-cell reverse transcription-PCR analysis revealed that TRPC1, TRPC3, TRPC4, TRPC5, TRPC6, and TRPC7 subunits were expressed in GnRH neurons. Therefore, it appears that kisspeptin depolarizes GnRH neurons through activating TRPC-like channels and, to a lesser extent, inhibition of Kir channels. These actions of kisspeptin contribute to the pronounced excitation of GnRH neurons that is critical for mammalian reproduction.

Kisspeptin signaling in the brain: Recent developments and future challenges

“…This approach evidenced that the stimulatory effects of Kp-10 on GnRH secretion require the activation of phospholipase-C (PLC), mobilization of intracellular Ca 2+ stores and recruitment of ERK1/2 and p38 kinases, while kisspeptininduced GnRH release was preserved in spite of the blockade of adenylate cyclase ( Figure 1); features that are grossly similar to those initially reported for KISS1R signaling using heterologous cell systems [9]. Likewise, recent studies involving electrophysiological recordings and/or calcium imaging in GnRH neurons have supported and extended those observations, showing that long-term excitation of GnRH neurons by kisspeptin is conveyed through a PLC/calcium dependent pathway regulating multiple ion channels, including the closing of potassium channels and the activation of non-selective cation (NSC) channels, which likely include canonical transient receptor potential (TRPC) channels [13][14][15].…”

Prostaglandin E 2 release from astrocytes triggers gonadotropin-releasing hormone (GnRH) neuron firing via EP2 receptor activation

“…This inward current had a linear voltage dependence from −120 to −40 mV and was suppressed at a mean value of −41.12 ± 3.54 mV (n = 4; Fig. 2 D2), suggesting the activation of a nonselective cation conductance (27,28). This value was also close to the membrane potential measured in current-clamp mode (−45.66 ± 1.68 mV, t test; P > 0.05; n = 7; Fig.…”

Melanin-concentrating hormone directly inhibits GnRH neurons and blocks kisspeptin activation, linking energy balance to reproduction

“…Kisspeptin and its receptor are critical for reproduction (10)(11)(12); both kisspeptin and kisspeptin receptor knockout mice fail to enter puberty, and humans with loss of function mutations in the kisspeptin receptor exhibit hypogonadotropic hypogonadism and are infertile (13)(14)(15). Mechanistically, kisspeptin is a potent activator of GnRH neurons (16)(17)(18)(19); it enhances pituitary gonadotropin release, triggering a cascade that is essential for entering puberty (13,20) and for maintaining ovulation and fertility (21).…”