Dual coupling of heterologously-expressed rat P2Y6 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 receptor previously reported to stimulate the phosphoinositide (PI) pathway. We have investigated its effect in neurones, by micro-injecting its cRNA. into dissociated rat sympathetic neurones and recording responses of N-type Ca2+ (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) mode 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; UTP, 20 +/- 1 nM. ATP and ADP (1 mu M) had no significant effect. Pertussis toxin (PTX) substantially (similar to 60%) reduced UTP-mediated inhibition in 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 significant 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 different G proteins. However, the P2Y(6) receptor displays a much higher sensitivity to its agonists than the P2Y(2) receptor in this expression system and higher than previously reported using other expression methods. The very high sensitivity to both UDP and UTP suggests that it might be preferentially activated by any locally released uridine nucleotides.