Redistribution and Increase in Cortical Inositol 1,4,5-Trisphosphate Receptors after Meiotic Maturation of the Mouse Oocyte

Mouse oocytes develop sensitivity to inositol 1,4,5-trisphosphate (IP₃) during oocyte maturation. We recently reported that a change in the organization of the endoplasmic reticulum (ER) during oocyte maturation may contribute to this enhanced sensitivity (Mehlmannet al.,1995,Dev. Biol.170, 607–615). Here, we investigated whether there is an increase in the number of available IP₃receptors after maturation and whether there is a redistribution of IP₃receptors similar to the redistribution of the ER that occurs during maturation. Western blot analysis of the IP₃receptor in oocytes and eggs demonstrated a 1.8-fold increase in immunoreactive mass of the IP₃receptor following oocyte maturation. Microinjection of the function-blocking monoclonal antibody 18A10 inhibited IP₃-induced Ca²⁺release in a concentration-dependent manner in both eggs and oocytes. More antibody was required to inhibit Ca²⁺release to the same extent in eggs compared to oocytes when both were injected with the same concentration of IP₃, suggesting that eggs contain a greater number of functional IP₃receptors. Immunolocalization of the IP₃receptor revealed that receptors were present in large clusters, 1–2 μm in diameter, in the cortex of the mature egg except in a ring-shaped band of cortex adjacent to the meiotic spindle. In contrast, receptor clusters were located around the entire cortex of the immature oocyte and were much smaller (<1 μm); larger patches were sometimes seen, but they did not display the same spherical organization as those in eggs. These results suggest that the number of cortical IP₃receptors increases during mouse oocyte maturation and that this increase may contribute to enhanced Ca²⁺release at fertilization.     

The influence of renal nerves on electrolyte excretion in conscious and anesthetized rats fed or fasted overnight

The role of the renal nerves in the electrolyte excretion of rats fed or fasted overnight was determined in conscious rats and anesthetized (Inactin) and surgically prepared rats. In conscious rats sodium excretion, as measured in a 1-h urine collection period after feeding or fasting overnight, was decreased with fasting with or without renal nerves. Renal nerve activity, as measured by norepinephrine turnover (inhibition of tyrosine hydroxylase by alpha-methyl-p-tyrosine), was not different between conscious fed or fasted rats and increased to the same extent in fed and fasted rats when anesthetized and surgically prepared. Anesthetized, surgically prepared rats infused with 5.0% glucose showed a denervation natriuresis if rats were fed overnight, but not if they had been fasted overnight. Potassium excretion in conscious and anesthetized rats was lower in fasted rats than fed rats with or without renal nerves. These data suggest (i) renal nerves are not involved in the renal response to an overnight fast in conscious rats, and (ii) in anesthetized, surgically prepared rat renal sympathetic tone is enhanced and denervation natriuresis occurs if rats are fed but not if fasted. Potassium excretion is a reflection of whether rats are fed or fasted and not whether they have renal nerves.     

IL-1 receptor antagonist release is regulated differently in human alveolar macrophages than in monocytes.

These studies compared the release of interleukin-1 receptor antagonist (IL-1 RA) from alveolar macrophages and peripheral blood monocytes. The cells were cultured in medium containing various amounts of heat-inactivated fetal calf serum (FCS), granulocyte-macrophage colony-stimulating factor (GM-CSF), lipopolysaccharide (LPS), and immunoglobulin G (IgG). In serum-free medium alone, IL-1 RA release was similar from macrophages and monocytes. Increasing FCS concentration caused a significant upregulation of IL-1 RA release in macrophages but not in monocytes. GM-CSF caused a small increase in both cell types. LPS caused downregulation of IL-1 RA release from monocytes but not from macrophages. IgG did not affect IL-1 RA release in either cell group. These studies demonstrate that regulation of IL-1 RA release is different in monocytes and macrophages.     

Retinoic acid blockade of imidazole-induced tyrosinase expression in B16 melanoma cultures: similar effects of the active retinoid and triiodothyronine

The effect of retinoic acid on the induction of tyrosinase (EC 1:14.18.1) by imidazole was determined in cultured B16/C3 melanoma cells. Retinoic acid could block the induction of enzyme activity within 3 hours of addition to the culture medium at a physiological concentration (10nM). The blockade was similar to that of 3,3',5-L-triiodothyronine (T3) already reported. mRNA hybridizable to a tyrosinase DNA probe was induced by imidazole while retinoic acid and T3 blocked that increase. These observations suggest that retinoic acid can mimic the action of T3 in B16 melanoma cells in culture.     

Unilateral naris occlusion and the rat accessory olfactory bulb

Blocking airflow through half of the nasal cavity during early life results in a 25% reduction in the size of the ipsilateral main olfactory bulb. The present study indicates that the size of the accessory bulb is relatively unaffected by the procedure.