EFFECTS OF CORPORA CARDIACA EXTRACT ON INTRACELLULAR 2ND MESSENGER LEVELS IN MALPIGHIAN TUBULES OF LOCUSTA-MIGRATORIA L

Intracellular levels of the second messenger molecules, cyclic adenosine 3′,5′-monophosphate (cAMP) and inositol 1,4,5-triphosphate (Ins-1,4,5-P3), have been measured in cells of Malpighian tubules of Locusta at various times following exposure to corpora cardiaca extracts with established diuretic activity. Such treatment effected a rapid initial rise in the levels of both second messengers compared with unstimulated control values; initial peaks being apparent at 6.5 ± 1.0 s (n = 4) and 5.2 ± 1.0 s (n = 5) for cAMP and Ins-1,4,5-P3, respectively. Following these initial increases, levels fell rapidly to near those of the non-stimulated controls, thereafter showing a more gradual increase; the latter being more sustained in the case of cAMP. Some variation was apparent in the pattern of these slower responses to corpora cardiaca extract. However, mean second messenger levels were significantly above non-stimulated control values at 60 and 300 s for cAMP and from 15 to 300 s, inclusive, for Ins-1,4,5-P3. The significance of these observations is discussed in relation to the endocrine control of ion and fluid transport across Malpighian tubules of Locvsta. © 1990.