ELECTROPHYSIOLOGICAL-ANATOMIC CORRELATES OF ATP-TRIGGERED VAGAL REFLEX IN THE DOG .3. ROLE OF CARDIAC AFFERENTS

To test the hypothesis that the asymmetry in the afferent traffic of t he intra-right atrium (RA) ATP-triggered vagal reflex is due to the st imulation by ATP of extrapulmonary (i.e., cardiac) vagal chemosensitiv e afferent terminals, ATP, adenosine, and capsaicin were given into th e canine RA and the aortic root (AR; n = 12); ATP and adenosine were a lso administered into the left, common carotid artery and the descendi ng aorta (n = 6). The negative chronotropic action [i.e., suppression of sinus node (SN) automaticity] of the test compounds and time to pea k effect (t(p)) were determined. Under baseline conditions, ATP given into the left common carotid artery had a relatively very small effect . ATP given into the descending aorta had no effect. In contrast, intr a-RA and intra-AR ATP markedly suppressed SN automaticity, the former less than the latter; the opposite was true for capsaicin. Intra-RA ad enosine was much less potent than intra-RA ATP. The t(p) of intra-RA A TP and intra-RA adenosine were larger than the t(p) of intra-AR ATP. P ulmonary denervation did not alter the effects of intra-RAATP, intra-A R ATP, or intra-AR capsaicin but almost abolished the effect of intra- RA capsaicin. Subsequent bilateral, but not left, cervical vagotomy ma rkedly reduce the effects of ATP and eliminated the difference between the effects of ATP and adenosine. In addition, t(p) of intra-RA ATP a nd intra-AR ATP increased substantially and were similar to t(p) of ad enosine. It was concluded that 1) ATP can stimulate vagal afferent ter minals not only in the lungs but also in the heart, 2) the latter cons titutes the vagal component of the negative chronotropic action of int ra-RA or intra-AR ATP on SN automaticity, and 3) the asymmetry in the vagal afferent traffic elicited by ATP in the heart (i.e., right vagal dominance) supersedes the symmetrical vagal afferent traffic triggere d by intrapulmonary ATP.