SUMMARY1. Previous work has.shown that the sodium efflux from the axons of Loligo forbesi increa 2. The increase in efflux in lithium was unaffected by ouabain but was abolished by removal of external calcium; in these respects it differed from the potassium-dependent sodium efflux which was abolished by ouabain but not reduced by removal of external calcium.3. Strontium but not magnesium could replace calcium in activating the ouabain-insensitive sodium efflux; lanthanum had an inhibitory effect.4. Replacing all the holine chloride or dextrose gave a rise in Na efflux which was abolishey ouabain but not by removal of external calcium.5. The rise in Na efflux resulting from partial replacement of NaCl by dextrose or choline chloride consisted of two components one of which was ouabain-insensitive and calcium-dependent and the other was inhibited by ouabain but calcium-insensitive.6. The ouabain-insensitive component of the Na efflux was activated by low concentrations of Na, Li or K but inhibited by high concentrations of Na and to a lesser extent Li. The inhibiting effect of high Na was of the kind expected if these ions displace calcium from an external site.7. The ouabain-insensitive component of the Na efflux was abolished by cyanide, had a Qlo of 2-7; and was roughly proportional to [Na]?. It was much more variable in magnitude than the ouabain-sensitive, potassiumdependent component of the sodium efflux. 8. The calcium influx increased five to fortyfold when external NaCl

SUMMARY1. Changes in ionized calcium in giant axons were followed by recording the light produced by injected aequorin.2. From the effect of injecting calcium buffers the internal concentration of ionized calcium was found to be about the same as in a mixture of 45 Ca EGTA: 55 free EGTA, i.e. about 04a1sM.3. After an axon had been exposedwto cyanide for 50-100 min the velocity of the aequorin reaction increased about 500 times. This effect, which could be reversed rapidly by removing cyanide, was probably brought about by release of calcium from an internal store.4. Injecting 30 tumole ATP per litre of axoplasm into a cyanide-poisoned axon caused a transient lowering of light intensity; oligomycin blocked the effect.5. Raising external cqicium or replacing external sodium by choline or lithium reversible increased the light produced by axons injected with aequorin.

By subjecting isolated adrenal medullary cells to intense electric fields of brief duration it is possible to gain access to the cell interior without impairing the ability of the cell to undergo exocytosis. After a single exposure to ~ field of 2kV/cm, ~=200 gsec, adrenal medullary cells behave as if their plasma membrane contains two pores of effective radius 2nm. At 37 ~ these 'equivalent pores' remain patent for up to lhr. The formation and stability of these 'pores' is not affected by the Ca content of the bathing solution. The 'pores' permit externally applied catecholamine and Ca-EGTA to equilibrate rapidly with the cell water.Cells rendered 'leaky' in K glutamate medium containing 5mM Mg-ATP and EGTA to give an ionized Ca close to 10-SM release less than i % of their total catecholamine. These same cells can release up to 30 % of their catecholamine when exposed to 10 s M Ca. This Ca-dependent release is unaffected by Cachannel blockers such as D600. Catecholamine release in response to a calcium challenge only seems to occur during the first few minutes whilst the Ca concentration is changing, and the extent of release depends onthe final Ca concentration achieved. Half-maximal release occurs at about 1 gM Ca, and this value is independent of the EGTA concentration used to buffer the ionized Ca. The relation between ionized Ca and catecholamine release is best fitted by a requirement for 2 Ca ions.Calcium-evoked release of catecholamine is associated with the release of dopamine-fi-hydroxylase (D/~H) but not lactate dehydrogenase. The ratio DflH/catecholamine released is the same as that in stimulated intact cells and perfused glands. The time course of appearance in the external medium of D/~H and catecholamine is identical. Transmission electron microscopy of 'leaky' cells exposed to 10 aM Ca reveals no marked differences from unstimulated intact cells. The cytoplasm of 'leaky' cells exposed to 10-5M Ca contains large membrane-bounded vacuoles. When secretion is caused to take place in the presence of horseradish peroxidase, this marker is found within the vacuoles.Ca-dependent release of both catecholamine and D/~H requires Mg-ATP. Cells equilibrated with Ca in the absence of Mg-ATP can be triggered to undergo exocytosis by the addition of Mg-ATP. In the absence of Mg, ATP alone is ineffective. Of a variety of other nucleotides tested, none is as effective as ATP. Mg-ATP affects the extent of exocytosis and not its apparent affinity for Ca.Replacement of glutamate as the major anion by chloride results in a marked reduction in Ca-dependent release of both catecholamine and D/~H. Chloride causes a small increase in Caindependent release of catecholamine, a large reduction in the extent of exocytosis, and a decrease in the apparent affinity of exocytosis for Ca. Of a variety of anions examined, their order of effectiveness at supporting Ca-dependent exocytosis is glutamate -> acetate -> C1-> Br > SCN -.Exocytosis is not obviously affected by replacing K by Na or sucrose or by altering the pH over the ra...

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