Isabella Mezzasoma

Molecular and binding characteristics of IP3 receptors in bovine spermatozoa

We have shown the presence of inositol 1,4,5‐triphosphate (IP3) receptors in bovine spermatozoa. These receptors are mainly localized and functionally associated with the acrosome region. Molecular characterization of these bovine IP3 receptors has shown that the functional size of the IP3 binding domain is a protein of 66 ± 2 kDa, in agreement with the size of both bovine adrenal cortex and bovine adrenal medullar chromaffin cells IP3 receptors. In contrast, bovine cerebellum IP3 receptor displays molecular weight of 220 ± 5 kDa, a value in agreement with data in the literature. Bovine IP3 receptors have a one‐affinity state characterized by a low affinity (Kd 750 nM) and a relatively high density (7.5 pmol/mg protein). They are functional and release internal calcium upon the binding of the second messenger. Moreover, the finding that the specific A1 adenosine receptor agonist R‐PIA elicits almost the same effect as IP3 might be of some help in understanding the physiological role of these inhibitory adenosine receptors in mammalian spermatozoa. Mol. Reprod. Dev. 56:527–533, 2000.

Polycyclic aromatic hydrocarbons enhance the production of phorbol 12-myristate 13-acetate-induced superoxide ions in human monocytes

Monocytes, separated from peripheral blood, preincubated with a mixture of polycyclic aromatic hydrocarbons (PAHs) show an enhanced production of superoxide ions (O2-.) when the cells are stimulated with phorbol 12-myristate 13-acetate (PMA, direct activator of protein kinase C). When opsonized-zymosan is used as a stimulus (receptor-dependent stimulus), no enhanced production of O2-. is observed. Superoxide production increases dose dependently up to a PAH concentration of 5 microg/ml. Although the effect was rather small (125-145% of the control value), it was significant and reproducible. Similar enhancing activity was also observed in the production of hydrogen peroxide (H2O2) excluding an inhibitory effect of PAHs on the enzyme superoxide dismutase (SOD). Since the effect is related to the concentration of PMA and in the absence of stimulus, the O2-. is undetectable in both the control and in the PAHs-treated cells, it is concluded that the over production of O2-. is due to an increased activity of the NADPH oxidase.