Effects of intestinal insulin‐like peptide on glucose catabolism in mealworm larval fat body in vitro: Dependence on extracellular Ca²⁺ for its stimulatory action

Abstract

In vitro hormonally induced variations of glucose catabolism in mealworm fat body tissue were examined by a microradiorespirometric method. An insulin-like peptide (ILP) extracted from the midgut of last larval instar mealworm larvae significantly modified glucose catabolism and was dependent on energy metabolism and on the Ca2+ concentration in the culture medium. Using two different labelled substrate molecules, the stimulatory effects of ILP (compared with those of mammalian insulin) on the relative use of the pentose cycle as opposed to the glycolytic-citric acid cycle by the mealworm fat body were measured in vitro. Metabolic variations were evaluated using either [1-14C]glucose or [6-14C]glucose as substrates. Time course and dose-response curves of ILP and the hormonally induced variations in total CO2 and 14CO2 kinetics were determined. Modification in the specific radioactivity kinetics of 14CO2 derived from [1-14C] glucose and [6-14C]glucose molecules under hormonal effects were observed. As demonstrated in in vivo studies, ILP stimulated the relative utilization of the pentose cycle. However, this effect was observed much more rapidly, but for a shorter time, with fat body in vitro. Mammalian insulin produced similar, but not identical effects. Variations in transmembranous Ca2+ cellular exchanges, induced by either EGTA, nifedipine, or calcium ionophore ionomycin included in the culture medium, indicated that the stimulatory effects of ILP depends on this cation.

Bombyxin gene expression in tissues other than brain detected by reverse transcriptionpolymerase chain reaction (RT-PCR) and in situ hybridization

“…In insects such as Apis mellifera [16] and Locusta migratoria [17], the insulin-related molecules exist in various tissues besides the brain. In addition, insulin-like activity of the insulin-related peptides has been shown in various insects such as Tenebrio molitor [18], Locusta [17] and Apis [19]. At present, no evidence has been presented for bombyxin to correspond to one of those insulinrelated peptides.…”

Relationships between adenylyl cyclase activity, glucose metabolism, and both intestinal insulin-like peptide and adipokinetic hormone in mealworm larval fat body

“…This effect was dependent both on the basal energy metabolism of target tissues and on the Ca2' concentration of the incubation medium used (Mtioui et al, 1993a). It was observed that ILP stimulated the relative utilization of the pentose cycle, as previously described from in vivo studies (Bounias et al, 1986).…”

“…Such effects may be induced in the fat body cells of Tepzebuio larvae by ILP binding. Another criterion for the participation of such ILP binding receptors is provided by the comparison of the specific radioactivity data (I4CO2 evolved from C,-glucose) obtained in the presence of increasing concentrations of ILP and Ca2' (Mtioui et al, 1993a). There is some evidence that the large number of complex pathways participating in the transduction of ILP effects require high energy production over a long time, and the pentose cycle appears to be a solution to this problem.…”

“…The optimal Ca2+ concentration of the physiological medium, required for maximum hormonal activation, was previously determined to correspond to 4 mM (Mtioui et al, 1993a;Candy et al, 1986). …”

F-actin, β-tubulin, aldolase, and fructose-1,6-bisphosphatase in heteropteran ovarioles—I. Immunocytochemical investigations of whole-mounted ovarioles

“…Biochemical studies have shown that the composition and concentration of the carbohydrates, amino acids, and lipids in the hemolymph undergo drastic changes depending on diet and hormonal conditions (e.g., Singh 1965: Sarcophaga ruficornis, Diptera; Fischl et al 1973: Vespa orientalis, Hymenoptera; Blatt and Roces 2001: Apis mellifera, Hymenoptera; Satake et al 2000: Bombyx mori, Lepidoptera; Thompson 1999Thompson , 2004: Manduca sexta, Lepidoptera; Mtioui et al 1993: Tenebrio molitor, Coleoptera). Moreover, in heteropterans, the carbohydrate concentration in the hemolymph is diet-dependent and varies widely (Canavoso and Rubiola 1998: Dipetalogaster maximus, Reduviidae).…”