Diadenosine polyphosphates activate a Ca2+-dependent K+-conductance in porcine aortic smooth muscle cells via P2-purinoceptors

Effects of the diadenosine polyphosphates P-1,P-3-diadenosine triphosphate (Ap3A), P-1,P-4-diadenosine tetraphosphate (Ap4A), P-1,P-5-diadenosine pent aphosphate (Ap5A) and P1,PG-diadenosine hexaphosphate (Ap6A) and of adenosi ne, ATP, ADP AMP, UTP on smooth muscle cells from porcine aorta were examin ed. Membrane voltages and cellular conductances were measured in the slow w hole cell configuration of the patch clamp technique. All four diadenosine polyphosphates, adenosine, AMP and ADP predominantly hyperpolarized membran e voltages with only occasional transient initial depolarizations whereas A TP and UTP led to sustained depolarizations. All four diadenosine polyphosp hates increased cellular conductances. The effects of Ap5A on membrane volt ages were almost completely inhibited by the putative P2-purinoceptor antag onist pyridoxal-phosphate-6-azophenyl-2',4'-di acid (PPADS, 10 mu mol/l) an d only partially reduced by the putative A(2)-purinoceptor antagonist 3,7-d imethyl-1-propragyl-xanthine (DMPX, 10 mu mol/l) or the Ap4A-receptor antag onist diinosine pentaphosphate (Ip5I, 10 mu mol/l). The adenosine-induced h yperpolarization was partially reduced by the putative A,-purinoceptor anta gonist 8-cyclopentyl-1,3-dipropargylxanthine (DPCPX, 0.1 mu mol/l) or by DM PX while PPADS or Ip5I were without effects. Ap5A-induced hyperpolarization s were inhibited by Ba2+ and clotrimazole but not by glibenclamide. We conc lude that diadenosine polyphosphates activate predominantly a Ca2+-dependen t K+-conductance in smooth muscle cells obtained from porcine aorta most li kely mediated via P2Y-purinoceptors and possibly partially also by Ap4A rec eptors. Copyright (C) 2000 S. Karger AG, Baser.