GAP JUNCTIONAL INTERCELLULAR COMMUNICATION OF BOVINE LUTEAL CELLS FROM SEVERAL STAGES OF THE ESTROUS-CYCLE - EFFECTS OF CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE

Cellular interactions mediated by both contact-dependent and contact-i ndependent mechanisms are probably important to maintain luteal functi on. The objective of the present study was to evaluate the role of cAM P in regulation of contact-dependent gap junctional intercellular comm unication (GJIC) of bovine luteal cells from several stages of luteal development. In experiment 1, corpora lutea (n = 5) from the mid-lutea l phase of the estrous cycle were dissociated with collagenase, and ce lls were preincubated in a medium with serum. Then the medium was chan ged to serum-free media containing a cAMP agonist (dbcAMP; 1 mM) or an tagonist (Rp-cAMPS; 0, 3, 10, 30, or 100 mu M). In experiment 2, corpo ra lutea from the early (n = 7), mid- (n = 6), and late (n = 6) luteal phases of the estrous cycle were dissociated and preincubated as in e xperiment 1, and luteal cells were then incubated with no treatment, L H (100 ng/ml), dbcAMP (1 mM), forskolin (1 mu M), Rp-cAMPS (100 mu M), or LH + Rp-cAMPS. After incubation of luteal cells with treatments fo r 18-24 h, media were collected for determination of progesterone and cAMP concentrations. Then the rare of GJIC was evaluated for selected cells (small luteal cells in contact with small luteal cells, and larg e luteal cells in contact with small luteal cells) by using the fluore scence recovery after photobleaching technique and laser cytometry. In experiment 1, dbcAMP increased (p < 0.01) but Rp-cAMPS (p < 0.05) dec reased GJIC between small luteal cells and between large and small lut eal cells. In addition, dbcAMP stimulated (p < 0.01) but Rp-cAMPS did not affect progesterone secretion. In experiment 2, treatments affecte d (p < 0.05) GJIC and progesterone production of luteal cells from the mid- and late but not from the early luteal phase of the estrous cycl e. GJIC between small luteal cells was increased (p < 0.01) by LH, dbc AMP, and forskolin. GJIC between large and small luteal cells was incr eased (p < 0.05) by dbcAMP and forskolin. Rp-cAMPS decreased (p < 0.01 ) GJIC between small luteal cells (mid-luteal phase) and between large and small luteal cells (mid- and late luteal phases). In addition, Rp -cAMPS inhibited (p < 0.05) the stimulatory effects of LH on GJIC betw een small luteal cells from the mid- and late luteal phases of the est rous cycle. For luteal cells from the mid- and late luteal phases, pro gesterone production was increased (p < 0.05) by LH, dbcAMP, forskolin , and LH + Rp-cAMPS, but was not affected by Rp-cAMPS. Across all stag es of the estrous cycle, cyclic AMP accumulation in media was greater (p < 0.05) in LH- and forskolin-treated cultures than in control cultu res and was greater (p < 0.01) in forskolin-treated than in LH-treated cultures. These data demonstrate that small and large luteal cells co mmunicate with each other and that the rate of GJIC is modulated by LH and cAMP, as has been shown previously for other cell types. Thus, cA MP appears to be involved in the regulation of GJIC within the bovine corpus luteum, which probably is an important mechanism for coordinati ng luteal cell function.