FHF-independent conduction of action potentials along the leak-resistant cerebellar granule cell axon

Neurons in vertebrate central nervous systems initiate and conduct sodium action potentials in distinct subcellular compartments that differ architecturally and electrically. Here, we report several unanticipated passive and active properties of the cerebellar granule cell’s unmyelinated axon. Whereas spike initiation at the axon initial segment relies on sodium channel (Nav)-associated fibroblast growth factor homologous factor (FHF) proteins to delay Nav inactivation, distal axonal Navs show little FHF association or FHF requirement for high-frequency transmission, velocity and waveforms of conducting action potentials. In addition, leak conductance density along the distal axon is estimated as o1% that of somatodendritic membrane. The faster inactivation rate of FHF-free Navs together with very low axonal leak conductance serves to minimize ionic fluxes and energetic demand during repetitive spike conduction and at rest. The absence of FHFs from Navs at nodes of Ranvier in the central nervous system suggests a similar mechanism of current flux minimization along myelinated axons

Cardiovascular maladaptation to exercise in young hypertensive patients

BACKGROUND: Impairment of the adaptive mechanisms that increase cardiac output during exercise can translate to a reduced functional capacity. We investigated cardiovascular adaptation to exertion in asymptomatic hypertensive patients, aiming to identify the early signs of cardiac and vascular dysfunction. METHODS AND RESULTS: We enrolled 54 subjects: 30 patients (45.1±11.9years, 19 males) and 24 age-matched healthy controls (44.4±9.6years, 14 males). Speckle-tracking echocardiography (STE) and echo-tracking were performed at rest and during exertion to assess myocardial deformation and arterial stiffness. RESULTS: E/E\u27 increased from rest to peak exercise more in patients than in controls (peak stage: p=0.024). Global longitudinal strain increased significantly from rest to peak stage in controls (p=0.011) whereas it remained unchanged in patients (p=0.777). Left atrial (LA) reservoir was significantly increased throughout the exercise only in controls (p=0.001) whereas it was almost unchanged in patients (p=0.293). LA stiffness was significantly higher in patients than in controls both at rest (p=0.023) and during exercise (p CONCLUSIONS: Our study showed a more pronounced maladaptation during exercise, with respect to rest, of the cardiovascular system with impaired cardiac-vessel coupling in hypertensive patients compared to healthy subjects. Exercise echocardiography implemented by STE and echo-tracking is invaluable in the early detection of these cardiovascular abnormalities