Origin of the after‐hyperpolarization that follows removal of depolarizing agents from the isolated superior cervical ganglion of the rat

Abstract

1 Potential changes in isolated rat superior cervical ganglia following addition and removal of depolarizing agents were recorded using a moving-fluid extracellular electrode system. 2 Ganglionic negativity produced by carbachol was followed by a pronounced ganglionic positivity on washing. This after-positivity was attributed to hyperpolarization of the ganglion cells since it was unaffected by crushing the postganglionic trunk. 3 The after-hyperpolarization was selectively depressed by (a) cooling (Q₁₀ 2·3), (b) metabolic inhibitors (cyanide, azide, 2,4-dinitrophenol), (c) reducing [K⁺]_o or substituting Cs⁺ for K⁺, (d) ouabain, and (e) substituting Li⁺ for Na⁺. This suggested a close dependence on active Na⁺ transport. 4 When K⁺ was restored to K⁺-free solution, or the preparation was warmed rapidly, or when metabolic inhibitors were washed away, the hyperpolarization was rapidly regenerated. The effect of restoring K⁺ indicated that the hyperpolarization was generated directly by the Na⁺ pump. 5 The hyperpolarization was not altered by replacing CI⁻ with isethionate, indicating that the voltage change produced by the Na⁺ current was not modified by passive CI⁻ movements. 6 Hexamethonium added to the washout fluid augmented the after-hyperpolarization, suggesting that there was a high (cationic) leak current due to continued receptor-activation on washing with normal Krebs solution. 7 The hyperpolarization was reduced by omission of Ca²⁺ and restored by addition of Mg²⁺. This was considered to result from changes in passive membrane permeability. 8 The time-course of post-carbachol hyperpolarization accorded with a Na⁺ extrusion process whose rate was directly proportional to [Na⁺]_i with a rate constant of 0·38 ± 0·02 min⁻¹ at 23–27° C. 9 With increasing concentrations of carbachol, the amplitude of the hyperpolarization increased in proportion to the preceding depolarization, but the rate constant of the hyperpolarization was unchanged. 10 The after-hyperpolarization was reduced in proportion to the depolarization by hexamethonium, but was not affected by atropine, hyoscine or tetrodotoxin. 11 A hyperpolarization also followed depolarization by acetylcholine or by EDTA in Ca²⁺-free solution. 12 Nicotine-depolarization was not followed by a hyperpolarization unless hexamethonium was added to the washout fluid. This was attributed to prolonged receptor-stimulation by nicotine. 13 It was concluded that the after-hyperpolarization was due to the electrogenic extrusion of Na⁺ accumulated in the ganglion cells during the preceding depolarization, with no involvement of specific muscarinic receptors. The relationship of this process to post-tetanic hyperpolarization and to other forms of drug-induced ganglionic hyperpolarization is discussed.