ELECTRICAL-PROPERTIES OF IRIDIAL ARTERIOLES OF THE RAT

When intracellular recordings were made from iridial arterioles, the c ells had membrane potentials of about -65 mV and perivascular nerve st imulation evoked a membrane depolarization. When these cells were labe led with lucifer yellow, all cells that responded to perivascular nerv e stimulation had the morphological characteristics of smooth muscle c ells. Cells with the morphological characteristics of endothelial cell s were never stained. When impaled with two separate recording electro des, the smooth muscle layer was shown to form an electrical syncytium with a membrane time constant of similar to 80 ms and an electrical l ength constant of similar to 900 mu m. At the ultrastructural level, a reas of close apposition were frequently observed between adjacent smo oth muscle cells and between adjacent endothelial cells. On the other hand, at contacts between smooth muscle and endothelial cells, the mem branes characteristically had much larger separations. The observation s show that individual smooth muscle cells are electrically coupled to their neighbors, but the morphological studies raise the possibility that in these arterioles the endothelial and muscle layers are electri cally separate.