P2Y2 nucleotide receptors expressed heterologously in sympathetic neurons inhibit both N-type Ca2+ and M-type K+ currents

The P2Y(2) 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 P2Y(2) 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 P2Y(2) cRNA, 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 P2Y(2) nucleotide receptors of N-type calcium currents in rat sympathetic neurones. Br J Pharmacol 121:849-851], UTP inhibited the Ca2+ current (/(Ca(N)) ) by up to 64%, with an IC50 of similar to 0.5 mu M. We now find that UTP also inhibited the K-M(+), current (/(K(M)) by up to 61 %, with an IC50 of similar to 1.5 mu M. UTP had no effect on either current in neurons not injected with P2Y(2) cRNA. Structure-activity relations for the inhibition of /(Ca(N)) and /(K(M)) in P2Y(2) cRNA-injected neurons were similar, with UTP greater than or equal to ATP > ITP >> GTP,UDP. However, coupling to these two channels involved different G-proteins: pretreatment with Pertussis toxin (PTX) did not affect UTP-induced inhibition of /(K(M)) but reduced inhibition of /(Ca(N)) by similar to 60% and abolished the voltage-dependent component of this inhibition. In unclamped neurons, UTP greatly facilitated depolarization-induced action potential discharges. Thus, the single P2Y(2) receptor can couple to at least two G-proteins to inhibit both Ca-N(2+) and K-M(+) channels with near-equal facility. This implies that the P2Y(2) receptor may induce a broad range of effector responses in the nervous system.