P2-receptor modulation of noradrenergic neurotransmission in rat kidney.
1. ATP has previously been shown to act as a sympathetic cotransmitter in the rat kidney. The present study analyses the question of whether postganglionic sympathetic nerve endings in the kidney possess P2-receptors which modulate noradrenaline release. Rat kidneys were perfused with Krebs-Henseleit solution containing the noradrenaline uptake blockers cocaine and corticosterone and the alpha2-adrenoceptor antagonist rauwolscine. The renal nerves were electrically stimulated, in most experiments by 30 pulses applied at 1 Hz. The outflow of endogenous noradrenaline (or, in some experiments, of ATP and lactate dehydrogenase) as well as the perfusion pressure were measured simultaneously. 2. The P2-receptor agonist adenosine-5'-O-(3-thiotriphosphate) (ATPgammaS, 3-30 microM) reduced the renal nerve stimulation (RNS)-induced outflow of noradrenaline (estimated EC50 =8 microM). The P2-receptor antagonist cibacron blue 3GA (30 microM) shifted the concentration-inhibition curve for ATPgammaS to the right (apparent pKB value 4.7). 3. Cibacron blue 3GA (3-30 microM) and its isomer reactive blue 2 (3-30 microM) significantly increased RNS-induced outflow of noradrenaline in the presence of the P1-receptor antagonist 8-(p-sulphophenyl)theophylline (8-SPT, 100 microM) by about 70% and 90%, respectively. The P2-receptor antagonist suramin (30-300 microM) only tended to enhance RNS-induced outflow of noradrenaline. When the nerves were stimulated by short pulse trains consisting of 6 pulses applied at 100 Hz (conditions under which autoinhibition is inoperative), reactive blue 2 did not affect the RNS-induced outflow of noradrenaline. 4. RNS (120 pulses applied at 4 Hz) induced the outflow of ATP but not of the cytoplasmatic enzyme lactate dehydrogenase. 5. ATPgammaS (3-30 microM) concentration-dependently reduced pressor responses to RNS at 1 Hz. Cibacron blue 3GA, reactive blue 2 as well as suramin also reduced pressor responses to RNS (maximally by 50 to 70%). 6. This study in rat isolated kidney, in which the release of endogenous noradrenaline was measured, demonstrates that renal sympathetic nerves possess prejunctional P2-receptors that mediate inhibition of transmitter release. These prejunctional P2-receptors are activated by endogenous ligands, most likely ATP, released upon nerve activity. Both, P2-receptor agonists and P2-receptor antagonists reduced pressor responses to RNS either by inhibiting transmitter release or by blocking postjunctional vasoconstrictor P2-receptors.
Bohmann
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Medizinische Universitätsklinik Freiburg, Innere Medizin IV, Germany.
von Kügelgen
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Rump
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D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure; D007668:Kidney / Q000294:innervation*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D014227:Triazines / Q000494:pharmacology
D018048:Receptors, Purinergic P2; D014227:Triazines; C022571:adenosine 5'-O-(3-thiotriphosphate); C012842:Cibacron Blue F 3GA; C031433:8-(4-sulfophenyl)theophylline; D000255:Adenosine Triphosphate; D013806:Theophylline; D007770:L-Lactate Dehydrogenase; D009638:Norepinephrine