title: The mechanism of increased postnatal heart rate and sinoatrial node pacemaker activity in mice.
abstract: Heart rate (HR) of mammalian species changes postnatally, i.e., HR of large animals including humans decreases, while HR in small animals such as mice and rats increases. To clarify cellular mechanisms underlying the postnatal HR changes, we performed in vivo HR measurement and electrophysiological analysis on sinoatrial node (SAN) cells in mice. The in vivo HR was ~320 beats min(-1) (bpm) immediately after birth, and increased with age to ~690 bpm at postnatal day 14. Under blockage of autonomic nervous systems, HR remained constant until postnatal day 5 and then increased day by day. The spontaneous beating rate of SAN preparation showed a similar postnatal change. The density of the L-type Ca(2+) current (LCC) was smaller in neonatal SAN cells than in adult cells, accompanied by a positive shift of voltage-dependent activation. Thus, the postnatal increase in HR is caused by both the increased sympathetic influence and the intrinsic activity of SAN cells. The different conductance and kinetics of LCC may be involved in the postnatal increase in pacemaker activity.
authors.affiliation: Department of Cell Physiology, Akita University Graduate School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Adachi
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Shibata
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Shinichi
authors.initials: S
authors.lastname: Sato
authors.forename: Susumu
authors.initials: S
authors.lastname: Fujisawa
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Ohba
authors.forename: Kyoichi
authors.initials: K
authors.lastname: Ono
mesh_terms: D000200:Action Potentials; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001683:Biological Clocks / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D006339:Heart Rate / Q000187:drug effects; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating; D007700:Kinetics; D008297:Male; D049990:Membrane Transport Modulators / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects / Q000294:innervation / Q000378:metabolism / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology
chemical_list: D020746:Calcium Channels, L-Type; D054815:Cyclic Nucleotide-Gated Cation Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D049990:Membrane Transport Modulators; D002118:Calcium