Movements of labelled sodium ions in isolated rat superior cervical ganglia

Open Access
Publisher Website
Google Scholar
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 (kC) for the desaturation curve at 25° C was 0·35 ± 0·01 min−1. An Arrhenius plot of log kC/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 kC 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 kC of 0·58 min−1. 6. Cyanide (2 m M), 2,4‐dinitrophenol (1 m M) and ouabain (1·4 m M) reduced kC 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.