GAP JUNCTION-MEDIATED CELL-TO-CELL COMMUNICATION IN BOVINE AND HUMAN ADRENAL-CELLS - A PROCESS WHEREBY CELLS INCREASE THEIR RESPONSIVENESS TO PHYSIOLOGICAL CORTICOTROPIN CONCENTRATIONS

We have studied the role of gap junction-mediated intercellular commun ication on the steroidogenic response of bovine (BAG) and human (HAC) adrenal fasciculo-reticularis cells in culture to corticotropin (ACTH) , Indirect immunofluorescence analyses showed that intact human and bo vine adreno-cortical tissue as well as HAC and BAC in culture expresse d the gap junction protein connexin43 (also termed alpha 1 connexin). Both HAC and BAC were functionally coupled through gap junctions as de monstrated by microinjection of a low molecular mass fluorescent probe , Lucifer yellow, The cell-to-cell transfer of the probe was blocked b y 18 alpha-glycyrrhetinic acid (GA), an inhibitor of gap junction-medi ated intercellular communication. GA markedly decreased the steroidoge nic response (cortisol production) of both HAC and BAC to low (10 pM) but not to high (5 nM) concentrations of ACTH, GA had no inhibitory ef fect on the steroidogenic response to 8 Br-cAMP (at either low or high concentrations) and did neither modify the binding of I-125-ACTH to i ts receptor nor the ACTH-induced cAMP production, BAC cultured at high or low cell densities (2.4 x 10(5) vs. 0.24 x 10(5) cells/cm(2)) exhi bited distinct levels of intercellular communication and were differen tly responsive to sub-maximal ACTH concentrations, The ACTH ED(50) val ues for cortisol production were 8.5 +/- 1.3 and 45 +/- 14 pM (P < 0.0 2) for BAC cultured at high and low density, respectively, In the pres ence of GA, there was a shift of the ACTH concentration-response curve s in the two culture conditions, The ACTH ED(50) of high density and l ow density cultured BAC increased 25- and 5-fold, respectively, and be came similar (220 +/- 90 and 250 +/- 120 pM). These results demonstrat e that gap junction-mediated communication between hormone-responsive and nonresponsive cells is one mechanism by which adrenal cells increa se their responsiveness to low ACTH concentrations.