Abstract
Studies were carried out on cat adrenal glands perfused in situ to determine the effects of magnesium (Mg2+) and the local anesthetic, tetracaine, on catecholamine secretion and calcium movement. The presence of tetracaine (3 x 10-4 M) or Mg2+(5 x 10-3 M) profoundly inhibited (> 90%) the rate of catecholamine release when calcium (Ca2+) was subsequently added to Ca2+-free Locke's solution or to Ca2+-free Locke's solution containing 56 mM KCl. Inhibition by tetracaine was detectable at concentrations as low as 3 x 10-6 M. The inhibitory effects of tetracaine and Mg2+ were reversed by raising the Ca2+ concentration in the perfusion fluid. Tetracaine, at concentrations as low as 1.5 x 10-6 M, depressed the secretory response to acetylcholine (ACh). When tetracaine and magnesium were employed at concentrations which produced nearly equivalent inhibition of the ACh response, excess Ca2+(8 and 16 mM) was more effective in reversing the Mg2+-induced depression. Both tetracaine (3 x 10-4 M) and Mg2+(5 x 10-3 M) markedly depressed calcium exchange between the gland and the perfusate. Tetracaine also decreased Ca45 uptake resulting from ACh stimulation. It is concluded that tetracaine and Mg2+ inhibit secretion by interfering with Ca2+ entry into the medullary chromaffin cells, presumably by an action at the cell membrane.
Footnotes
- Received May 16, 1966.
- Accepted September 21, 1966.
- © 1967 by The Williams & Wilkins Company
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