DIFFERENTIAL EXPRESSION OF GAP JUNCTION CONNEXINS IN ENDOCRINE AND EXOCRINE GLANDS

We have investigated the expression of three gap junction proteins and their corresponding mRNAS by secretory cells of a variety of endocrin e and exocrine rat glands. By immunostaining cryostat sections (indire ct immunofluorescence) with antibodies against connexins (Cx) 26, 32, and 43 and by hybridizing total glandular RNA (Northern blot) with cRN As for these proteins, we have found that several endocrine glands (pi tuitary, parathyroid, pancreatic islets, and adrenal) express Cx43, va riable levels of Cx26, and no Cx32, whereas several exocrine glands (l acrimal gland, salivary glands, pancreas, prostate, and seminal vesicl e) express high levels of Cx32 and variable levels of Cx26, but no Cx4 3. Thus, different sets of proteins comprise the pp junctions of endoc rine and exocrine glands. Together with the findings that an endocrine gland (thyroid) that discharges secretory products extracellularly be fore releasing them in the vascular compartment expresses both Cx43 an d Cx32 and that an exocrine gland (preputial gland) that has a pheromo nal role expresses Cx43, these observations suggest that the different ial expression of gap junction connexins may be required to specify th e endocrine or exocrine differentiation of a secretory cell.