Conduction of the Cardiac Impulse III. Characteristics of very slow conduction

摘要: The excitability of short segments (5–7 mm) bundles canine Purkinje fibers was depressed by exposure to 15–18 mM K+, K+ plus 5 x 10-6 epinephrine or norepinephrine, low and Na+. segment in the center chamber a three-chamber bath; ends bundle were exposed normal Tyrode solution. Each method depression resulted slow probably decremental conduction with an effective velocity middle about 0.05 m/sec, one-way block, two-way block summation graded responses region. action potential (the response) differs from its response applied stimuli. A second active depolarization can be evoked cathodal stimulation during much response. is graded. may depend on excitatory events similar those responsible for component cardiac potential. It suggested that propagate, at least decrementally, which rapid, Na+-dependent upstroke absent, cause reentrant excitation so doing.