Ionic basis of noradrenaline depolarization and hyperpolarization in toad dorsal root ganglia neurones

Abstract

The membrane conductance and reversal potential were estimated for neurones in toad dorsal root ganglia with intracellular recording technique during depolarization or hyperpolarization induced by noradrenaline (NA). The effects of blocking agents for potassium or calcium ion current on NA-induced membrane potential responses were observed as well.

The NA depolarization was accompanied by a 32.6% decrease of membrane conductance. In a few neurones, the membrane conductance showed an initial increase and a following decrease. The NA hyperpolarization was associated with an increase of membrane conductance by 16.2%. The mean reversal potential of NA depolarization was -88.5 ± 0.9mV. The NA hyperpolarization responses were nullified at -89 to -92 mV of membrane potential. TEA superfusion enhanced NA depolarization amplitude by 73.7 ± 11.9% and depressed NA hyperpolarization amplitude by 40.5%. CsCl (intracelluar injection) increased phenylephrine depolarization by 34.5 %. MnCl₂ superfusion decreased the amplitudes of NA depolarization by 50.5 ± 9.9%, and of NA hyperpolarizalion by 89.5±4.9% respectively. The results suggest that depolarization or hyperpolarization induced by NA might be mediated by the alteration of K or Ca channels.

Keywords

noradrenaline / dorsal root ganglion / α-adrenoceptor / membrane conductance

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