Movements of labelled sodium ions in isolated rat superior cervical ganglia

Abstract

1. Isolated rat superior cervical ganglia were incubated in Krebs solution containing ²⁴Na and carbachol for 4 min at 25° C. They were then washed at 3° C for 15 min to remove extracellular ²⁴Na and the efflux of residual intracellular ²⁴Na stimulated by warming to 25° C. 2. During the 15 min wash at 3° C desaturation curves became exponential with a rate constant of 0·012 ± 0·001 min⁻¹ (n = 24). This was assumed to represent loss of intracellular ²⁴Na, and initial uptake of ²⁴Na was calculated therefrom by back‐extrapolation to zero wash‐time. After 4 min in ²⁴Na + 180 μ M carbachol intracellular [²⁴Na] so calculated was 61·6 ± 3·1 m M (n = 18), representing 83% labelling of intracellular Na. In the absence of carbachol intracellular [²⁴Na] was 10·0 ± 0·5 m M, representing 49% labelling. Extracellular Na was labelled by > 90% after 4 min in ²⁴Na. The apparent rate constant for washout of extracellular ²⁴Na was 0·6 min⁻¹ at 3° C and 0·95 min⁻¹ at 25° C. 3. The loss of the residual intracellular ²⁴Na during temperature stimulation was interpreted quantitatively in terms of an exponential decline of the bulk of intracellular ²⁴Na with an extrusion rate constant of 0·39 ± 0·1 min⁻¹ (n = 18), efflux being delayed by passage through the extracellular space with an effective rate constant of 0·8–1·2 min⁻¹. 4. The peak rate constant (k^C) for the desaturation curve at 25° C was 0·35 ± 0·01 min⁻¹. An Arrhenius plot of log k^C/T° K⁻¹ yielded a two‐stage linear regression with a transition at 20° C. Activation energies of 8 and 31 kcal. mole⁻¹ were calculated above and below this transition respectively. 5. Omission of K from the 25° C temperature‐stimulating solution reduced k^C by 62%. The K‐sensitive component of extrusion rate constant was a hyperbolic function of [K]_e with half‐saturation at 5·6 m M‐[K]_e and maximum k^C of 0·58 min⁻¹. 6. Cyanide (2 m M), 2,4‐dinitrophenol (1 m M) and ouabain (1·4 m M) reduced k^C by 50–90%. The half‐maximally inhibiting concentration of ouabain was about 60 μ M. 7. Substitution of sucrose, Li or choline for external Na did not reduce the extrusion rate of ²⁴Na in either 6 m M‐[K]_e or 0 m M‐[K]_e. Li stimulated ²⁴Na extrusion in Na‐free, K‐free solution. 8. The properties of the ganglionic Na pump deduced from rates of temperature‐stimulated ²⁴Na extrusion accord with the view that the ganglion hyperpolarization observed after Na loading by exposure to nicotinic depolarizing agents results from electrogenic Na extrusion. A comparable hyperpolarization is observed after temperature stimulation following Na loading.