Differential expression of inositol 1,4,5-trisphosphate receptor types 1, 2, and 3 in rat myometrium and endometrium during gestation

The regulation of the phospholipase C (PLC) and the expression of inositol 1,4,5-trisphosphate receptors (IP(3)Rs) in terms of mRNA, proteins, and bin ding capacity were examined in the rat myometrium and endometrium at midges tation (Day 12) and at term (Day 21) comparatively to the estrogen-treated tissues (Day 0). In both uterine tissues, the production of inositol phosph ates mediated by carbachol as well as by AlF4- was enhanced with advancing gestation. (3)[H]IP3 binding sites in membranes also increased during pregn ancy (Day 21 > Day 12 > Day 0), The mRNAs encoding for three isoforms of IP 3R as well as their corresponding proteins, IP3R-1, IP3R-2, and IP3R-3 were coexpressed, albeit to different extents, in the myometrium and endometriu m. The expression of IP(3)Rs increased with advancing gestation, except for IP3R-2 that increased only in the endometrium at term. Thus, the pregnancy -related upregulation of the PLC cascade coincided with an increase in the expression of IP(3)Rs. The difference noted between the two uterine tissues suggests that IP(3)Rs may have cell-specific functions.