Endocrinology, Vol 132, 2654-2658, Copyright © 1993 by Endocrine Society

ARTICLES

Stimulation by Mn2+ and inhibition by Cd2+, Zn2+, Ni2+, and Co2+ ions of luteinizing hormone exocytosis at an intracellular site

JS Davidson, SE Franco and RP Millar
Department of Chemical Pathology, University of Cape Town Medical School, South Africa.

Direct intracellular effects of the divalent cations Mn2+, Cd2+, Co2+, Ni2+, and Zn2+ on pituitary hormone exocytosis in a permeabilized cell system have not previously been investigated. We examined the effects of these ions on LH exocytosis in primary sheep pituitary cells permeabilized with Staphylococcal alpha-toxin. Mn2+ ions strongly stimulated LH release from permeabilized, but not intact, cells. Mn(2+)- stimulated LH release was ATP-dependent and sensitive to N-ethyl maleimide, indicating that it represents true exocytosis. Hormone release triggered by Ca2+ was inhibited by Cd2+, Zn2+, Co2+, and Ni2+ ions. Half-maximal inhibition of Ca(2+)-stimulated LH release was observed with 10 microM Cd2+, 30 microM Zn2+, 0.3 mM Co2+, and 1 mM Ni2+. With the same order of potency these ions inhibited LH release stimulated by Ba2+, Mn2+, or phorbol ester plus cAMP, suggesting that they inhibit exocytosis at an intracellular site common to all these stimuli.

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