Cell-to-cell communication in cultured neonatal rat myocardial cells

The sensitivity of the cell-to-cell communication pathway to interventions designed to elevate intracellular Ca, diminish intracellular pH and deplete cellular energy levels was tested. Transfer of iontophoretically injected Lucifer Yellow (LY) or dicarboxy fluorescein (DCF) to neighboring cells was monitored via fluorescence microscopy. Intervention designed to raise intracellular calcium included (number of cells injected indicated parenthetically): 1) 10 μM (4 LY) and 25 μM (4 LY) A23187, 2) 1 mM ouabain plus 10 μM monensin (4 DCF, 11 LY), and 3) 1 mM ouabain plus 10 mM caffeine (9 DCF, 5 LY). Transfer was always observed during exposure to A23187. In ouabain and monensin (up to 51 minutes), LY transferred in 91% of the cases. DCF in 0%. In ouabain and caffeine (up to 2 hrs), DCF transferred in 100% of the cases, LY in 83%. In the presence of 5 mM KCN and 20 μM deoxyglucose, used to compromise cellular energetics, transfer of LY and DCF occurred initially but was lost in most cultures over time, 15 to 30 minutes. Loss of transfer capacity was reversible. Simultaneous energy depletion and intracellular calcium elevation (5 mM KCN plus 20 mM deoxyglucose plus 10 μM monensin) resulted in a reversible loss of cell coupling within 8-15 minutes (n = 6). Intracellular pH was altered using 20 mM acetate at pH 6.6 or 6.3. The resting membrane potential fell under these conditions to -20 mV; however, transfer of LY occurred in 90% of the cases (n = 20). Rate of transfer appeared to be slow compared to control conditions. In conclusion, cell-to-cell communication in cultured neonatal rat myocardial cells is maintained in the face of intervention which are expected to increase intracellular calcium, or decrease intracellular pH and energy stores. Only when energy stores were depleted in the face of calcium loading conditions was dye-transfer consistently compromised.