title: Delayed activation of the cardiac pacemaker current and its dependence on conditioning pre-hyperpolarizations.
abstract: The activation time course of the pacemaker current if in Purkinje fibres during hyperpolarizations is s-shaped, which requires kinetics more complex than first order. Large, short hyperpolarizations preceding a fixed activating test pulse cause the current trace to shift to the left on the time-axis, as if a delay in if activation were removed, and eventually lead to a current trace which is a simple exponential and activates with no delay during a test pulse. Current traces before and after a relatively short and small prepulse will superimpose after a time translation. Further increasing prepulse amplitude and/or duration gives current traces that cannot be made to superimpose with the test current trace. The channel opening can be described by first order kinetics only if a delay in current activation is introduced.
mesh_terms: D000818:Animals; D002417:Cattle; D004562:Electrocardiography; D004573:Electrolytes / Q000378:metabolism; D006329:Heart Conduction System / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D011690:Purkinje Fibers / Q000502:physiology*
chemical_list: D004573:Electrolytes; D007473:Ion Channels