P2Y(2) NUCLEOTIDE RECEPTORS EXPRESSED HETEROLOGOUSLY IN SYMPATHETIC NEURONS INHIBIT BOTH N-TYPE CA2-TYPE K+ CURRENTS( AND M)

The P2Y(2) receptor is a uridine/adenosine triphosphate (UTP/ ATP)-sen sitive G-protein-linked nucleotide receptor that previously has been r eported to stimulate the phosphoinositide signaling pathway. Messenger RNA for this receptor has been detected in brain tissue. We have inve stigated the coupling of the molecularly defined rat P2Y(2) receptor t o neuronal N-type Ca2+ channels and to M-type K+ channels by heterolog ous expression in rat superior cervical sympathetic (SCG) neurons. Aft er 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 sympath etic neurones. Br J Pharmacol 121:849-851], UTP inhibited the Ca2+ cur rent (/(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 t o 61 %, with an IC50 of similar to 1.5 mu M. UTP had no effect on eith er current in neurons not injected with P2Y(2) cRNA. Structure-activit y 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 diff erent G-proteins: pretreatment with Pertussis toxin (PTX) did not affe ct UTP-induced inhibition of /(K(M)) but reduced inhibition of /(Ca(N) ) by similar to 60% and abolished the voltage-dependent component of t his inhibition. In unclamped neurons, UTP greatly facilitated depolari zation-induced action potential discharges. Thus, the single P2Y(2) re ceptor 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 P2 Y(2) receptor may induce a broad range of effector responses in the ne rvous system.