CONTACT-DEPENDENT INTERCELLULAR COMMUNICATION OF BOVINE LUTEAL CELLS IN CULTURE

Mammalian gap junctions permit exchange of nutrients, ions, and regulatory molecules of less than 1.5 kDa among contacting communication-competent cells and may be important for regulation of luteal function and maintenance of luteal homeostasis. The present studies were designed to evaluate gap junction-mediated intercellular communication between bovine luteal cells in culture. Using a dye-coupling technique along with interactive laser cytometry, selected luteal cells were studied for the rate of contact-dependent fluorescence redistribution after photobleaching. The rate of communication, reported as the rate of fluorescence recovery (percentage per min), was determined for steroidogenic cells as follows: 1) small luteal cells contacting only small luteal cells, 2) large luteal cells contacting only small luteal cells, and 3) large luteal cells contacting only large luteal cells. In addition, the effects of known regulators of luteal function [LH, prostaglandin F2-alpha (PGF), and forskolin] on the rate of intercellular communication were determined. Small luteal cells communicated rapidly with each other, exhibiting an initial rate of fluorescence recovery of 4.1 +/- 0.1%/min (n = 187). The rate of small cell-small cell communication was unaffected by LH and PGF. For large luteal cells contacting small luteal cells, however, LH and PGF stimulated (P < 0.02) the rate of communication compared with no hormone [1.6 +/- 0.2 (n = 18) and 1.5 +/- 0.6 (n = 20) vs. 0.8 +/- 0.3%/min (n = 27), respectively]. LH and PGF in combination, however, did not enhance the rate (0.6 +/- 0.2%/min; n = 19) of large cell-small cell communication. In contrast, forskolin significantly stimulated both small cell-small cell and large cell-small cell communication rates compared with no forskolin [34% increase (n = 48) and 50% increase (n = 23), respectively]. Large luteal cells did not communicate with each other under any condition tested. Transmission electron microscopy revealed the presence of numerous gap junction-like structures in bovine luteal cells in culture. These data suggest that luteal cells are capable of intercellular communication and that the rate of communication may be influenced by hormones. Contact-dependent intercellular communication among luteal cells may, therefore, play a significant role in the regulation of luteal function.