Adenine nucleotides inhibit recombinant N-type calcium channels via G protein-coupled mechanisms in HEK 293 cells; involvement of the P2Y13 receptor-type.

1: N-type Ca²⁺ channel modulation by an endogenous P2Y receptor was investigated by the whole-cell patch-clamp method in HEK 293 cells transfected with the functional rabbit N-type calcium channel. 2: The current responses (I_Ca(N)) to depolarizing voltage steps were depressed by ATP in a concentration-dependent manner. Inclusion of either guanosine 5'-O-(3-thiodiphosphate) or pertussis toxin into the pipette solution as well as a strongly depolarizing prepulse abolished the inhibitory action of ATP. 3: In order to identify the P2Y receptor subtype responsible for this effect, several preferential agonists and antagonists were studied. Whereas the concentration-response curves of ADP and adenosine 5'-O-(2-thiodiphosphate) indicated a higher potency of these agonists than that of ATP, a,ß-methylene ATP, UTP and UDP were considerably less active. The effect of ATP was abolished by the P2Y receptor antagonists suramin and N⁶-(2-methylthioethyl)-2-(3,3,3-trifluoropropylthio)-ß,?-dichloromethylene-ATP, but not by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid, 2'deoxy-N⁶-methyladenosine-3',5'-diphosphate or 2-methylthio AMP. 4: Using reverse transcription and polymerase chain reaction, mRNA for the P2Y₁, P2Y₄, P2Y₆, P2Y₁₁ and P2Y₁₃ receptor subtypes, but not the P2Y₂, and P2Y₁₂ subtypes, was detected in HEK 293 cells. 5: Immunocytochemistry confirmed the presence of P2Y₁, and to a minor extent that of P2Y₄, but not of P2Y₂ receptors. 6: Hence, it is tempting to speculate that P2Y₁₃ receptors may inhibit N-type Ca²⁺ channels via the ß? subunits of the activated G_i protein.British Journal of Pharmacology (2004) 141, 141-151. doi:10.1038/sj.bjp.0705588 [ABSTRACT FROM AUTHOR]