MODULATION OF PROTEIN-KINASE-C BY ADENOSINE - INVOLVEMENT OF ADENOSINE A(1) RECEPTOR-PERTUSSIS TOXIN-SENSITIVE NUCLEOTIDE-BINDING PROTEIN SYSTEM

The objective of this study was to determine whether adenosine A(1) or A(2) receptor was responsible for the regulation of protein kinase C (PKC) in porcine coronary artery and its coupling to G-protein. Endoth elium denuded arterial rings were incubated with PDBu (200 nM) in the presence or absence of adenosine receptor agonists and antagonists for 1 day. Following incubation, the arterial rings were contracted with increasing concentrations of endothelin-1 (ET-1) (10(-10)-10(-7) M). A rteries incubated with PDBu alone failed to produce contraction in res ponse to ET-1. On the contrary, inclusion of A(1) receptor agonist ENB A at 10(-9) M in the incubation media with PDBu protected against the PDBu induced blunting of the ET-1 contractions by 50%. Incubation with ENBA alone increased ET-1 dependent contractions by about 2 fold. Inc lusion of A(1) receptor antagonist, N0861 at 10(-6) M along with PDBu and ENBA, completely blocked the protective effect of ENBA against the PDBu induced attenuation of ET-1 contractions. N0861 also completely blocked the increase in ET-1 contractions in the arterial rings incuba ted with ENBA alone. Another A(1) receptor antagonist DPCPX also produ ced similar results as N0861. On the contrary, arterial rings incubate d with relatively specific A(2) receptor agonist CGS 21680 at 10(-4) M did not produce any protection against PDBu induced blunting of the E T-1 contractions. Incubation with CGS 21680 alone also did not signifi cantly alter the ET-1 contractions. Interestingly, inclusion of A(2) r eceptor antagonist DMPX at 10(-4) M in the incubation media along with CGS 21680 mimicked the effects of ENBA alone i.e. produced protection against PDBu and enhanced ET-1 contractions, Incubation of the arteri es with ENBA alone caused an accumulation of PKC levels, whereas, incu bation with CGS 21680 had no significant effect on PKC levels. To stud y the coupling of adenosine receptor with G-protein, the tissue was in cubated for one day with cholera (CT) or pertussis toxin (PT) in the p resence or absence or ENBA and PDBu as described above. Incubation wit h PT blocked the protective effect of ENBA against PDBu as well as the elevation of ET-1 response when incubated with ENBA alone. On the con trary, incubation with CT did not produce any significant effect on EN BA responses, These results indicate that PKC is modulated by adenosin e via A(1) adenosine receptors and through a PT sensitive G-protein.