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 (Q(10) 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 Cl(-) with isethionate, indicating that the voltage change produced by the Na(+) current was not modified by passive Cl(-) 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 Ca(2+) and restored by addition of Mg(2+). 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 degrees 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.