GAP JUNCTIONAL INTERCELLULAR COMMUNICATION OF BOVINE LUTEAL CELLS FROM SEVERAL STAGES OF THE ESTROUS-CYCLE - EFFECTS OF PROSTAGLANDIN-F2-ALPHA, PROTEIN-KINASE-C AND CALCIUM

Cellular interactions mediated by both contact-dependent and contact-i ndependent mechanisms are probably important to maintain luteal functi on. The present studies were performed to evaluate the effects of lute otropic and luteolytic hormones, and also intracellular regulators, on contact-dependent gap junctional intercellular communication (GJIC) o f bovine luteal cells from several stages of luteal development. Bovin e corpora lutea (CL) from the early, mid and late luteal phases of the estrous cycle were dispersed with collagenase and incubated with no t reatment, LH, PGF or LH + PGF (Experiment 1), or with no treatment, or agonists or antagonists of protein kinase C (TPA or H-7) or calcium ( A23187 or EGTA; Experiment 2). After incubation, media were collected for determination of progesterone concentrations. Then the rate of GJI C was evaluated for small luteal cells in contact with small luteal ce lls, and large luteal cells in contact with small luteal cells by usin g the fluorescence recovery after photobleaching technique and laser c ytometry. Luteal cells from each stage of the estrous cycle exhibited GJIC, but the rate of GJIC was least (P<0.05) for luteal cells from th e late luteal phase. LH increased (P<0.05) GJIC between small luteal c ells from the mid and late but not the early luteal phase. PGF increas ed (P<0.05) GJIC between small luteal cells from the mid luteal phase and diminished (P<0.05) LH-stimulatory effects on GJIC between small l uteal cells from the late luteal phase. Throughout the estrous cycle, TPA decreased ((P<0.05) the rate of GJIC between large and small, and between small luteal cells, and A23187 decreased (P<0.05) the rate of GJIC between large and small luteal cells. LH and LH + PGF, but not PG F alone increased (P<0.05) progesterone secretion by luteal cells from the mid and late luteal phases. Agonists or antagonists of PKC or cal cium did not affect progesterone secretion by luteal cells. These data demonstrate that both luteal cell types communicate with small luteal cells, and the rate of communication depends on the stage of luteal d evelopment. LH and PGF affect GJIC between small luteal cells during t he fully differentiated (mid-luteal) and regressing (late luteal) stag es of the estrous cycle. In contrast, at all stages of luteal developm ent, activation of PRC decreases GJIC between small and between large and small luteal cells, whereas calcium ionophore decreases GJIC only between large and small luteal cells. Luteotropic and luteolytic hormo nes, and intracellular regulators, may be involved in regulation of ce llular interactions within bovine CL which Likely is an important mech anism for coordination of luteal function.