SYNCYTIAL ORGANIZATION OF CULTURED RAT MESANGIAL CELLS

To investigate communication competence of cultured rat mesangial cells, Lucifer yellow transfer was studied using microinjection and scrape-loading techniques. Both methods yielded results indicating considerable gap junctional communication between cultured mesangial cells. Gap junctional communication between mesangial cells was upregulated by adenosine 3',5'-cyclic monophosphate (cAMP). Conversely, cell-to-cell communication was attenuated by exposure to the tumor promoter phorbol myristate acetate, the Ca ionophore ionomycin, reduced oxygen intermediates, and cell acidification. Expression of voltage-gated calcium channels by mesangial cells was studied microspectrofluorimetrically using fura-2 fluorescence. KCl-induced depolarization, BAY K 8644, and readdition of calcium to Ca-free depolarizing medium all produced a nifedipine-inhibitable increase in cytosolic calcium concentration. The existence of voltage-gated calcium channels in communication-competent cells suggests the possibility of propagation of depolarizing signals across the syncytium. This was studied by microapplication of KCl to the microenvironment of a single cell and monitoring fura-2 fluorescence in remote cells. This maneuver resulted in propagating calcium waves in communication-competent monolayers; calcium waves could not be evoked in monolayers exposed to an alkanol-type gap junction uncoupler, octanol. It is concluded that cultured rat mesangial cells form a syncytium capable of propagating calcium transients from a single depolarized cell to its coupled neighbors.