Meeting Abstract
P1.32 Tuesday, Jan. 4 Changes in intracellular calcium concentration in crustacean (Callinectes sapidus) Y-organs: relation to the hemolymphatic ecdysteroid titer CHEN, H.-Y.; DILLAMAN, R.M.; ROER, R.D.; WATSON, R.D.*; University of Alabama at Birmingham; University of North Carolina at Wilmington; University of North Carolina at Wilmington; University of Alabama at Birmingham rdwatson@uab.edu
Secretion of ecdysteroid molting hormones by crustacean Y-organs is negatively regulated (inhibited) by molt-inhibiting hormone (MIH), a neuropeptide produced by neurosecretory cells in the eyestalks. The effect of MIH on Y-organs is mediated by one or more cyclic nucleotide second messengers. In addition, extant data indicate that ecdysteroidogenesis is positively regulated (stimulated) by intracellular Ca++. Our previous results showed that ablating the eyestalks from blue crabs (Callinectes sapidus), to remove the endogenous source of MIH and activate Y-organs, led to an increase in Ca++ in Y-organ cells; associated with the increase in intracellular Ca++ was a significant increase in the hemolymphatic ecdysteroid titer. In experiments reported here, we measured Ca++ levels in Y-organ cells (using a fluorescent calcium indicator, Fluo-4) and ecdysteroid levels in hemolymph (using radioimmunoassay) during selected stages of a natural molting cycle. Calcium fluorescence in Y-organ cells increased >6-fold between intermolt (stage C) and late premolt (stage D3) (P<0.05), then dropped during postmolt (stage A) to a level indistinguishable from that seen in intermolt (P>0.05). Changes in the hemolymphatic ecdysteroid titer followed a similar pattern, rising from 1.4 ng/ml in intermolt (stage C) to 357.1 ng/ml in late premolt (stage D3), and then dropping to 30.3 ng/ml in postmolt (stage A). The above results are consistent with the hypothesis that ecdysteroidogenesis is stimulated by an increase in intracellular Ca++. Additional findings from our lab indicate intracellular Ca++ may be linked to enhanced ecdysteroidogenesis through activation of cyclic nucleotide phosphodiesterase.
