Abstract

Leptin can exert its potent appetite-suppressing effects via activation of hypothalamic proopiomelanocortin (POMC) neurons. It depolarizes POMC neurons via activation of a yet unidentified nonselective cation current. Therefore, we sought to identify the conductance activated by leptin using whole-cell recording in EGFP-POMC neurons from transgenic mice. The TRPC channel blockers SKF96365 (1-[β-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride), flufenamic acid, and 2-APB (2-aminoethyl diphenylborinate) potently inhibited the leptin-induced current. Also, lanthanum (La³⁺) and intracellular Ca²⁺ potentiated the effects of leptin. Moreover, the diacylglycerol-permeable analog OAG (2-acetyl-1-oleoyl-sn-glycerol) failed to activate any TRPC current. Using a Cs⁺-gluconate-based internal solution, the leptin-activated current reversed near −20 mV. After replacement of external Na⁺ and K⁺ with Cs⁺, the reversal shifted to near 0 mV, and the I/V curve exhibited a negative slope conductance at voltages more negative than −40 mV. Based on scRT-PCR, TRPC1 and TRPC4–7 mRNA were expressed in POMC neurons, with TRPC5 being the most prevalent. The leptin-induced current was blocked by the Jak2 inhibitor AG490, the PI3 kinase inhibitor wortmannin, and the phospholipase C inhibitors, U73122 and ET-18-OCH3. Notably, we identified PLCγ1 transcripts in the majority of POMC neurons. Therefore, leptin through a Jak2–PI3 kinase–PLCγ pathway activates TRPC channels, and TRPC1, 4, and 5 appear to be the key channels mediating the depolarizing effects of leptin in POMC neurons.