Cardiac nociceptors and ischemia: role of sympathetic afferents in cat.

In total, 86 units were recorded from T2 and T3 left thoracic rami of cat. These receptors were located on the circumflex coronary artery, anterior descending coronary artery, and its adjacent myocardial regions. The conduction velocity of these fibres was in the range of "C" (0.5 to 1.8 m/s) and "A delta" (5.96 to 17 m/s) fibres. Out of these 86 units, only 28 units were activated by coronary occlusion. The average resting frequency of the spontaneous unit was 0.8 +/- 0.06 impulses/s which increased to 35 +/- 4.8 impulses/s on mechanical probing. In order to examine whether the units sensitive to coronary occlusion were also responsive to algesic agents, some of these units were studied applying lactic acid, bradykinin, prostaglandins, and nicotine. It was observed that these ischemia-sensitive units are also sensitive to lactic acid (10 units), bradykinin (16 units), prostaglandins (12 units), and nicotine (15 units). These ischemia-sensitive units are presumably nociceptors and activated by algestic agents that cause cardiac ischemic pain.