BIDIRECTIONAL ELECTRICAL COMMUNICATION BETWEEN SMOOTH-MUSCLE AND ENDOTHELIAL-CELLS IN THE PIG CORONARY-ARTERY

Using strips of the left descending branch of the pig coronary artery in vitro, we show that smooth muscle cells are hyperpolarized by isopr oterenol, a beta-agonist, independently of the presence or absence of intact endothelium. This hyperpolarization is transmitted to the linin g endothelial cells in intact coronary strips. On the contrary, the cu ltured endothelial cells, without contact with smooth muscles, are not hyperpolarized by the beta-agonist. This shows that, in addition to t he hyperpolarizations that flow from the endothelium to the media in r esponse to kinins, electrical signals are also transmitted in the oppo site direction, from the smooth muscles to the lining endothelial cell s. In an attempt to test whether electrical coupling through gap junct ions is implicated in the transmission of hyperpolarizations between t he endothelial and the smooth muscle cells, we used halothane, a gap j unction uncoupler. We observed that halothane does not inhibit the tra nsmission of kinin hyperpolarizations from the endothelium to the smoo th muscles, whereas it inhibits the transmission of isoproterenol hype rpolarization in the reverse direction.