Abstract
Abstract. Secretion of ecdysteroids by the prothoracic glands of the migratory locust, Locusta migratoria L., is enhanced in vitro by tris(hydroxymethyl)aminomethane (tris) in a dose‐dependent manner. Glands from larvae on the second day of the penultimate stadium are most sensitive. This action of tris depends on the uptake of calcium; increased production of ecdysteroid does not occur in the presence of cadmium, verapamil or TMB‐8, or in calcium‐free media. The concentration of unbound Ca2+, [Ca2+]i, in the cytoplasm is measured with the aid of FURA 2/AM. Tris causes a rise of [Ca2+]i that is fully suppressed by lanthanum and partially by nitrendipine. Two antagonists of IP3 receptors elicit mutually opposite effects: heparin blocks, whereas 2‐APB accelerates, the rise in [Ca2+]i. Ryanodine exerts only a slight effect. It is proposed that tris activates locust prothoracic glands in a Ca2+‐dependent manner that exhibits many similarities to the transduction pathway of prothoracicotropic hormone.
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