1 The effect of Li on catecholamine release by cat isolated retrogradely perfused adrenal gland was investigated. Replacement of Na (1 19 mM) by Li in the Krebs solution evoked a progressive increase in the spontaneous release of catecholamines that reached a maximum within 45 min and was Cadependent. This response was specific for Li, since sucrose or choline used as osmotic substitutes for Na, failed to increase the spontaneous release of catecholamines by the adrenal gland. 2 In glands perfused with Li-Krebs for 30 min a sharp secretory response was observed when Li was replaced by sucrose or choline; no such an effect was seen when Li was replaced by Na. 3 Partial replacement of Na by sucrose, in ouabain (10-4M, 10 min) pretreated glands perfused with normal Krebs induced a sharp increase in the catecholamine output whilst replacement by Li produced a significantly lower response. 4 Reintroduction of Ca (2.5 mM, 2 min) in glands previously perfused with Ca-free, Mg-containing Li-Krebs, evoked a sharp increase in catecholamine release. No such an effect was seen when the glands were perfused with Ca-free normal, choline-or sucrose-Krebs. 5 The release of catecholamines evoked by Ca reintroduction in glands previously perfused with Cafree Li-Krebs was directly dependent on the Li concentration and the length of time of the Li loading period. 6 In summary, our results indicate that Li accumulates in the cells and can partially substitute Na in the Na-Ca counter-transport system at the plasma membrane of the chromaffin cell.

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