Dual coupling of heterologously-expressed rat P2Y(6) nucleotide receptors to N-type Ca2+ and M-type K+ currents in rat sympathetic neurones

1 The P2Y(6) receptor is a uridine nucleotide-specific G protein-linked rec eptor previously reported to stimulate the phosphoinositide (PI) pathway. W e have investigated its effect in neurones, by micro-injecting its cRNA. in to dissociated rat sympathetic neurones and recording responses of N-type C a2+ (I-Ca(N)) and M-type K+ (I-K(M)) currents. 2 In P2Y(6) cRNA-injected neurones, UDP or UTP produced a voltage-dependent inhibition of ICB(N) by similar to 53% in whole-cell (disrupted-patch) mod e and by similar to 73% in perforated-patch mode; no inhibition occurred in control cells. Mean IC50 values (whole-cell) were: UDP, 5.9 +/- 0.3 nM; UT P, 20 +/- 1 nM. ATP and ADP (1 mu M) had no significant effect. Pertussis t oxin (PTX) substantially (similar to 60%) reduced UTP-mediated inhibition i n disrupted patch mode but not in perforated-patch mode. 3 Uridine nucleotides also inhibited I-K(M) in P2Y(6) cRNA-injected cells ( by up to 71% at 10 mu M UTP; perforated-patch). Mean IC50 values were: UDP, 30 +/- 3 nM; UTP, 115 +/- 12 nM. ATP (10 mu M) again had no effect. No sig nificant inhibition occurred in control cells. Inhibition was PTX-resistant . 4 Thus, the P2Y(6) receptor, like the P2Y(2) subtype studied in this system , couples to both of these two neuronal ion channels through at least two d ifferent G proteins. However, the P2Y(6) receptor displays a much higher se nsitivity to its agonists than the P2Y(2) receptor in this expression syste m and higher than previously reported using other expression methods. The v ery high sensitivity to both UDP and UTP suggests that it might be preferen tially activated by any locally released uridine nucleotides.