P2Y2Nucleotide Receptors Expressed Heterologously in Sympathetic Neurons Inhibit Both N-Type Ca2+and M-Type K+Currents

Open Access
Publisher Website
Google Scholar
Abstract
The P2Y2 receptor is a uridine/adenosine triphosphate (UTP/ATP)-sensitive G-protein-linked nucleotide receptor that previously has been reported to stimulate the phosphoinositide signaling pathway. Messenger RNA for this receptor has been detected in brain tissue. We have investigated the coupling of the molecularly defined rat P2Y2 receptor to neuronal N-type Ca2+ channels and to M-type K+channels by heterologous expression in rat superior cervical sympathetic (SCG) neurons. After the injection of P2Y2cRNA, UTP inhibited the currents carried by both types of ion channel. As previously reported [Filippov AK, Webb TE, Barnard EA, Brown DA (1997) Inhibition by heterologously expressed P2Y2nucleotide receptors of N-type calcium currents in rat sympathetic neurones. Br J Pharmacol 121:849–851], UTP inhibited the Ca2+ current (ICa(N)) by up to 64%, with an IC50 of ∼0.5 μm. We now find that UTP also inhibited the K+M current (IK(M)) by up to 61%, with an IC50 of ∼1.5 μm. UTP had no effect on either current in neurons not injected with P2Y2 cRNA. Structure–activity relations for the inhibition ofICa(N) and IK(M)in P2Y2 cRNA-injected neurons were similar, with UTP ≥ ATP > ITP ≫ GTP,UDP. However, coupling to these two channels involved different G-proteins: pretreatment withPertussis toxin (PTX) did not affect UTP-induced inhibition of IK(M) but reduced inhibition of ICa(N) by ∼60% and abolished the voltage-dependent component of this inhibition. In unclamped neurons, UTP greatly facilitated depolarization-induced action potential discharges. Thus, the single P2Y2 receptor can couple to at least two G-proteins to inhibit both Ca2+N and K+M channels with near-equal facility. This implies that the P2Y2 receptor may induce a broad range of effector responses in the nervous system.