title: The hyperpolarisation-activated current, I(f), is not required for pacemaking in single cells from the rabbit atrioventricular node.
abstract: The atrioventricular node (AVN) is vital for cardiac function. One of its properties is that it can act as a pacemaker for the ventricles if the sinoatrial node fails. This study investigates the role of the hyperpolarisation-activated inward current (I(f)) in generating pacemaker activity in morphologically normal single cells isolated from the rabbit AVN. Whole-cell patch-clamp recordings show that 80%-90% of AVN myocytes do not possess I(f), but nevertheless generate spontaneous action potentials with normal pacemaker depolarisations before each action potential upstroke. We have termed this type of cell "type 1". A small proportion (10%-20%) of spontaneously active AVN cells (type 2) do exhibit I(f). A 100 nM solution of isoprenaline increased the action potential rate of type 1 cells by 31%. In these cells isoprenaline did not activate any I(f) whereas in type 2 cells it clearly increased the amplitude of I(f). Manganese at 2 mM also increased the amplitude of I(f) in type 2 cells, but did not reveal I(f) in type 1 cells. We conclude that, whilst I(f) may play a role in modulating pacemaker activity in type 2 cells, in the majority of AVN cells (type 1) pacemaker depolarisation normally occurs in the complete absence of I(f). Furthermore, the inability of both isoprenaline and Mn to reveal I(f) in type 1 cells suggests that I(f) channels may be absent in these cells.
authors.affiliation: Department of Physiology, School of Medical Sciences, Bristol, UK.
authors.forename: J
authors.initials: J
authors.lastname: Hancox
authors.forename: A
authors.initials: A
authors.lastname: Levi
mesh_terms: D000818:Animals; D001283:Atrioventricular Node / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002469:Cell Separation; D004553:Electric Conductivity; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008345:Manganese / Q000494:pharmacology; D011817:Rabbits
chemical_list: D008345:Manganese; D007545:Isoproterenol; D002118:Calcium