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1α,25-Dihydroxyvitamin D(3) (1,25D(3)) is critical for the maintenance of normal reproduction since reduced fertility is observed in vitamin D-deficient male rats. The aim of this study was to investigate the effect of 1,25D(3) in 30-day-old rat testicular plasma membrane targets (calcium uptake and gamma-glutamyl transpeptidase (GGTP) activity), as well as to highlight the role of protein kinases in the mechanism of action of 1,25D(3). The results demonstrated that 1,25D(3) induced a fast increase in calcium uptake in rat testis through a nongenomic mechanism of action. This effect was dependent on PKA, PKC and MEK. Moreover, ionic channels, such as ATP- and Ca(2+)-dependent K(+) channels and Ca(2+)-dependent Cl(-) channels, are involved in the mechanism of action. The use of BAPTA-AM showed that [Ca(2+)](i) was also implicated, and the incubation with digoxin produced an increase in (45)Ca(2+) uptake indicating that the effect of 1,25D(3) may also result from Na(+)/K(+)-ATPase inhibition. In addition, 1,25D(3) was able to increase the GGTP activity. Considered together, our results indicate a PKA/PKC/MEK-dependent 1,25D(3) pathway as well as ionic involvement leading to (45)Ca(2+) uptake in immature rat testis. These findings demonstrate that 1,25D(3) stimulates calcium uptake and increases GGTP activity which may be involved in male reproductive functions.

The search for novel natural molecules with insecticide potential has become a necessity more than an alternative. Understanding the mode of action of candidate molecules is a crucial step towards the development of new bioinsecticides. The present study focused on the neurotoxicity of Canavalia ensiformis urease, a natural insecticide, in cockroaches and revealed interferences on the cholinergic, octopaminergic and GABA-ergic pathways as part of its entomotoxic mode of action.

1α,25-Dihydroxyvitamin D(3) (1,25D(3)) is the active metabolite of vitamin D(3) and the major calcium regulatory hormone in tissues. The aim of this work was to investigate the mechanism of action of 1,25D(3) on (45)Ca(2+) uptake in Sertoli cells from 30-day-old rats. Results showed that 10(-9) and 10(-12) M 1,25D(3) increased the rate of (45)Ca(2+) uptake 5 and 15 min after hormone exposure and that 1α,25(OH)(2) lumisterol(3) (JN) produced a similar effect suggesting that 1,25D(3) action occurs via a putative membrane receptor. The involvement of voltage-dependent calcium channels (VDCC) in 1,25D(3) action was evidenced by using nifedipine, while the use of Bapta-AM demonstrated that intracellular calcium was not implicated. Moreover, the incubation with ouabain and digoxin increased the rate of (45)Ca(2+) uptake, indicating that the effect of 1,25D(3) may also result from Na(+)/K(+)-ATPase inhibition. In addition, we demonstrated that the mechanism underlying the hormone action involved extracellular signal-regulated kinase (ERK) and protein kinase C (PKC) activation in a phospholipase C-independent way. Furthermore, a local elevation of the level of cAMP, as demonstrated by incubating cells with dibutyryl cAMP or a phosphodiesterase inhibitor, produced an effect similar to that of 1,25D(3), and the inhibition of protein kinase A (PKA) nullified the hormone action. In conclusion, the stimulatory effect of 1,25D(3) on (45)Ca(2+) uptake in Sertoli cells occurs via VDCC, as well as PKA, PKC, and ERK activation. These protein kinases seem to act by inhibiting Na(+)/K(+)-ATPase or directly phosphorylating calcium channels. The Na(+)/K(+)-ATPase inhibition may result in Na(+)/Ca(2+) exchanger activation in reverse mode and consequently induce the uptake of calcium into the cells.

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