Characterization of alpha 2-adrenoceptors which increase potassium conductance in rat locus coeruleus neurones.
Intracellular recordings were made from locus coeruleus neurones in a slice of rat pons superfused in vitro. A single-electrode voltage-clamp amplifier was used to measure membrane currents. Superfusion of the slice with clonidine (3-100 nM) or noradrenaline (100 nM-100 microM), or brief application of noradrenaline from a pipette by a pressure pulse, caused dose-dependent membrane hyperpolarizations. Phenylephrine (10 microM) and isoprenaline (10 microM) were ineffective. The hyperpolarizations were accompanied by a decrease in neurone input resistance. The hyperpolarization evoked by pressure ejection of noradrenaline could be reversed by membrane polarization to -110 mV. Clonidine and noradrenaline caused a membrane current which was linearly related to membrane potential between -50 and -120 mV, being outward at resting levels and reversing at -110 mV. The concentration-response curves for clonidine and noradrenaline were shifted rightwards in a parallel manner by alpha 2-adrenoceptor antagonists. The antagonist KeS estimated from the degree of shift were: RX 781094 9 nM, yohimbine 14 nM, phentolamine 20 nM and piperoxane 49 nM. These experiments indicate that in locus coeruleus neurones an increase in potassium conductance results from activation of alpha 2-adrenoceptors similar to those characterized on peripheral neurones.
Williams
J T
JT
Henderson
G
G
North
R A
RA
D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008125:Locus Coeruleus / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*
D007473:Ion Channels; D011942:Receptors, Adrenergic, alpha; D003000:Clonidine; D011188:Potassium; D009638:Norepinephrine; D010646:Phentolamine