title: Hypoxia inhibits the changes in action potentials and ion channels during primary culture of neonatal rat ventricular myocytes.
abstract: Action potentials of rat ventricular myocytes are progressively shortened after birth within several weeks mainly due to a progressive increase in transient outward potassium current (I(to)). On the supposition that an elevation in blood oxygen after birth may contribute to such developmental change, we studied effects of long-term exposure to hypoxia on changes in cardiac action potentials and I(to). Single ventricular myocytes isolated from day-old neonatal rat hearts were cultured in normoxic condition (21% O(2)) for 15 days and served as control. To test the influence of long-term exposure to hypoxia, O(2)tension was reduced to 7.5% at day 6 during culture. In 15-day cells cultured in normoxia, action potential duration (APD) was shortened by 44% (n=11) compared with 5-day cells (n=10); cell capacitance was increased to 2.0-fold. I(to)density was increased by 189-265% (n=11) at voltage levels from -20 to 50 mV without any changes in the kinetics of current inactivation. In 15-day cells cultured in hypoxia, APD was shortened only by 16% (n=6) from control; the increment of cell capacitance was 2.1-fold (n=6). The I(to)increment was limited to 53% (n=8); both inactivation and its recovery of the current was apparently slowed due to the amplification of the slower component. These results suggest that the developmental augmentation of I(to)expression during culture requires oxygen and the increase in I(to)and cell hypertrophy are likely regulated independently.
authors.affiliation: Department of Circulation, Research Institute of Environmental Medicine, Nagoya, 464-01, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kamiya
authors.forename: W
authors.initials: W
authors.lastname: Guo
authors.forename: K
authors.initials: K
authors.lastname: Yasui
authors.forename: J
authors.initials: J
authors.lastname: Toyama
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000332:Aerobiosis; D000818:Animals; D000831:Animals, Newborn; D015687:Cell Hypoxia / Q000502:physiology*; D002478:Cells, Cultured; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D009206:Myocardium / Q000166:cytology; D015737:Nisoldipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D013779:Tetrodotoxin; D015737:Nisoldipine