These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Patch-clamp analysis in canine cardiac Purkinje cells of a novel sodium component in the pacemaker range.
    Author: Rota M, Vassalle M.
    Journal: J Physiol; 2003 Apr 01; 548(Pt 1):147-65. PubMed ID: 12588904.
    Abstract:
    A putative Na+ component playing a role in the initiation and maintenance of spontaneous discharge in Purkinje fibres was studied by means of the whole-cell patch-clamp technique in canine cardiac single Purkinje cells. In 4 mM [K+]o, during depolarising clamp steps, a slowly inactivating current appeared at approximately -58 mV, negative to the threshold for the fast Na+ current (INa; approximately -50 mV). During depolarising ramps, the current underwent inward rectification with a negative slope region that began at approximately -60 mV. The current underlying the negative slope increased during faster ramps, decreased as a function of time when the initial depolarising ramp was over, decreased during depolarisations positive to approximately -35 mV and was much larger than the current during the symmetrical repolarising ramp. Increasing biphasic ('oscillatory') voltage ramps required much smaller currents at a holding potential (Vh) of -60 mV than at -80 mV and were associated with a marked decrease in slope conductance. At Vh -50/-40 mV, the oscillatory ramp currents and superimposed pulse currents reversed direction. The negative slope in the I-V relation as well as the change in current direction at -50/-40 mV were markedly reduced by tetrodotoxin (15 microM) and lidocaine (lignocaine, 100 microM) and therefore are due to a slowly inactivating Na+ current, labelled here INa3. Lower [K+]o (2.7 mM) reduced the steady state slope conductance as well as the current in the diastolic range, and increased as well as shifted INa3 in a negative direction. High [K+]o had the opposite effects. Cs+ (2 mM) and Ba2+ (2 mM) reduced the initial current during depolarising ramps but not INa3. In current-clamp mode, current-induced voltage oscillations elicited action potentials through a gradual transition between diastolic depolarisation and upstroke, consistent with the activation of INa3. Thus, the initiation and maintenance of spontaneous discharge in Purkinje strands appear to involve a voltage- and K+-dependent decrease in K+ conductance as well as the activation of a voltage- and time-dependent inward Na+ current (INa3) with slow inactivation kinetics.
    [Abstract] [Full Text] [Related] [New Search]