Depolarization of rat locus coeruleus neurons by adenosine 5'-triphosphate.
Intracellular recordings were performed in a pontine slice preparation of the rat brain containing the locus coeruleus. The enzymatically stable P2-purinoceptor agonist alpha,beta-methylene ATP increased the firing rate without altering the amplitude or shape of action potentials; the afterhyperpolarization following a spike was not changed either. When locus coeruleus neurons were hyperpolarized by current injection in order to prevent spontaneous firing, alpha,beta-methylene ATP produced depolarization and a slight increase in the apparent input resistance. A combined application of kynurenic acid and bicuculline methiodide failed to alter the alpha,beta-methylene ATP-induced depolarization, and tetrodotoxin only slightly depressed it. A gradual shift of the membrane potential by hyperpolarizing current injection led to a corresponding decrease, but no abolition or reversal of the alpha,beta-methylene ATP effect. In the hyperpolarized region, the current-voltage curve of alpha,beta-methylene ATP came into close approximation with, but did not cross, the control curve. Elevation of the external K+ concentration, or the intracellular application of Cs+ by diffusion from the microelectrode, depressed the response to alpha,beta-methylene ATP; external tetraethylammonium was also inhibitory. External Ba2+ and Cs+ had no effect or only slightly decreased the alpha,beta-methylene ATP-induced depolarization. A low Na+, or a low Ca2+ high Mg2+ medium, as well as the presence of Co2+ in the medium, markedly reduced or even abolished the depolarization by alpha,beta-methylene ATP. ATP itself did not produce consistent changes in the membrane potential or input resistance. However, in the presence of the P1-purinoceptor antagonist 8-cyclopentyl-1,3-dipropylxanthine, ATP consistently increased the firing rate and evoked an inward current. In conclusion, P2-purinoceptor activation appears to depolarize locus coeruleus neurons by inhibiting a persistent potassium current, and at the same time opening calcium-sensitive sodium channels or calcium-sensitive non-selective cationic channels.
Harms
L
L
Department of Pharmacology, University of Freiburg, F.R.G.
Finta
E P
EP
Tschöpl
M
M
Illes
P
P
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D008125:Locus Coeruleus / Q000187:drug effects / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D014970:Xanthines; D013779:Tetrodotoxin; D000255:Adenosine Triphosphate; D012964:Sodium; C051360:1,3-dipropyl-8-cyclopentylxanthine; D008274:Magnesium; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium