α‐Adrenoceptor Agonist‐Induced Stimulation of Na‐Ca Exchange in Rabbit Abdominal Aorta a

The Na-Ca antiporter couples translocation of Caz+ with the movement of Na+ in the opposite direction. In many tissues, the Na-Ca antiporter has been found to be electrogenic and voltage ~ensitivel-~ and to exchange three Na ions for each Ca ion transported across the cellular membrane.4 Therefore, in depolarized cells, the antiporter can exchange Ca:+ with Nq+. Although the activity of the Na-Ca antiporter is known to be influenced by [Cg'], ATP, and certain exogenous agent^,^^^.^ there has been as yet no demonstration of hormonal or neuronal regulation of Na-Ca exchange in smooth muscle. This may be due to alterations in the function of the antiporter during the preparation of isolated cells or membranal vesicle^.^.' The present investigation was designed (a) to measure Na-Ca exchange in pieces of tissue instead of isolated cells or membranal vesicles, (b) to determine whether agonists stimulate Na: -Ca:+ exchange, and (c) whether such stimulation is sensitive to changes in cell membrane potential.