The Cardiac Pacemaker Current if

Pacemaker Current if. Since the hyperpolarization-activated current, if, was originally associated with the diastolic depolarization phase of action potential in the sinoatrial (SA) node in 1979, its central role in the generation and control of pacemaker activity has become increasingly clear through a series of experimental findings, some of which have substantially modified the pre-existing theories of cardiac pacemaking and its modulation by the autonomic transmitters. Thus, the pacemaker current of Purkinje fibers, formerly described as a deactivating pure potassium (K) current, was found to be in fact, like the nodal if, inward and activating on hyperpolarization. Furthermore, in SA node cells, as well as mediating rhythm acceleration induced by catecholamines, if was found to underlie the slowing effect of low acetylcholine (ACh) concentrations, in contrast with the generally accepted hypothesis that activation of a K conductance is the main process responsible for cardiac slowing. A final, atypical property of if recently demonstrated concerns the activating action exerted on if by intracellular cAMP. Unlike that on other voltage-gated, cAMP-modulated cardiac channels, this action is independent of phosphorylation and involves a direct binding of cAMP to if channels. (J Cardiovasc Electrophysiol, Vol. 3, pp. 334–344, August 1992)     

Spinal Cord Stimulation (SCS) in Peripheral Ischemic Pain

Between 1982 and 1987,45 patients suffering from painful symptomatology caused by peripheral vascular disease, not curable by medical or surgical therapy, were implanted with epidural neurological stimulators. Measurements used in evaluating the effectiveness of the method were pain control, walking distance, and development of trophic problems. With most patients, we noted a satisfactory and long-lasting degree of pain control. Walking distance increased to a surprising degree. Trophic lesions smaller than 3 sq cm healed, while lesions of greater size required amputation of the limb. Transcutaneous oxygen tension (TcpO₂) was used to study the efects of SCS on peripheral circulation in implanted patients. In addition, TcpO₂ was calculated in 15 patients before and during the percutaneous test to predict the efectiveness of SCS. Regression of painful symptomatology was achieved only in patients whose TcpO_2b improved during the course of the testing. Therefore, this method provides an objective measure for the implantation of a neurostimulator