Kisspeptin depolarizes gonadotropin-releasing hormone neurons through activation of TRPC-like cationic channels

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 +/- 0.6 mV and EC50 of 2.8 +/- 0.2 nM. Under voltage-clamp conditions, kisspeptin induced an inward current of 18.2 +/- 1.6 pA ( V-hold = -60 mV) that reversed near -115 mV in GnRH neurons. The more negative reversal potential than E-K(+) ( -90 mV) was caused by the concurrent inhibition of barium- sensitive, inwardly rectifying ( Kir) potassium channels and activation of sodium-dependent, nonselective cationic channels (NSCCs). Indeed, reducing extracellular Na+ ( to 5 mM) essentially eliminated the kisspeptin-induced inward current. The current-voltage relationships of the kisspeptin-activated NSCC currents exhibited double rectification with negative slope conductance below -40mV 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-[beta-[3-( 4- methoxyphenyl) propoxy]- 4- methoxyphenethyl]- 1H- imidazole hydrochloride), and Cd2+, but not by lanthanum ( 100 mu 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.