Endothelial and smooth muscle cells hyperpolarized by bradykinin are not dye coupled

The membrane potential of endothelial and neighboring (0.1 mm) smooth muscle cells of pig coronary arteries were simultaneously recorded with two microelectrodes. The membrane potential of endothelial cells was -40 +/- 4 mV (n = 9). In these cells bradykinin (250 nM), an endothelium-dependent vasodilator, evoked a transient hyperpolarization (14 +/- 2 mV, n = 9) resembling those already observed in smooth muscles. The similarity between the electrical signal of pre- and postmyoendothelial junctions suggested an electrical coupling between endothelial and smooth muscle cells. However, the injection of the fluorescent dye Lucifer yellow in the recorded cell proved that the cell was endothelial, and in addition, the injection demonstrated the absence of dye coupling between endothelial and smooth muscle cells. Moreover the injection of electrical pulses (0.05-3.5 nA) in the endothelial cell never evoked any electrical response in the smooth muscle. By contrast, the smooth muscle cells were electrically coupled-together. These results do not support the idea that the endothelial cell hyperpolarization caused by bradykinin is transmitted to smooth muscle cells by electrotonic spreading.