MgATP‐Stimulated Release of Luteinizing Hormone Releasing Hormone from Isolated Hypothalamic Granules: Evidence for a Selective Requirement for Monovalent Cations

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Abstract
The kinetics and monovalent ion requirements of the MgATP-stimulated release of LHRH from isolated hypothalamic granules are characterized. LHRH granules were obtained from homogenates of hypothalami of adult male rats by differential centrifugation and then incubated in buffered media containing KCl. Under these conditions, the pH optimum for the MgATP-stimulated release of LHRH was between 7.5 and 8.0; the rate of release was linear for the first 5 min of incubation; and the magnitude of the release was a saturable function of KCl concentration. When the K in the incubation mixture was replaced with various monovalent cations (Li+, Na+, Cs+, choline, or tetraethylammonium), the magnitude of the MgATP-stimulated release of LHRH was inversely related to the size of the cation; release in the presence of Li+ was 12%, whereas release in the presence of tetraethylammonium was o% of the total LHRH. When the chloride in the incubation mixture was replaced with various monovalent anions (Br-, I-, or isethionate), the magnitude of the MgATP-stimulated release of LHRH was not related to the size of the anion. Moreover, inclusion of anion transport inhibitors in the incubation mixture did not affect LHRH release, suggesting that anion transport was not required for the MgATP-stimulated release of LHRH. The MgATP-stimulated release of LHRH from isolated hypothalamic granules involves an enzymatic event and this release process does not have a selective requirement for monovalent cations.

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