title: Functional embryonic cardiomyocytes after disruption of the L-type alpha1C (Cav1.2) calcium channel gene in the mouse.
abstract: The L-type alpha(1C) (Ca(v)1.2) calcium channel is the major calcium entry pathway in cardiac and smooth muscle. We inactivated the Ca(v)1.2 gene in two independent mouse lines that had indistinguishable phenotypes. Homozygous knockout embryos (Ca(v)1. 2-/-) died before day 14.5 postcoitum (p.c.). At day 12.5 p.c., the embryonic heart contracted with identical frequency in wild type (+/+), heterozygous (+/-), and homozygous (-/-) Ca(v)1.2 embryos. Beating of isolated embryonic cardiomyocytes depended on extracellular calcium and was blocked by 1 microm nisoldipine. In (+/+), (+/-), and (-/-) cardiomyocytes, an L-type Ba(2+) inward current (I(Ba)) was present that was stimulated by Bay K 8644 in all genotypes. At a holding potential of -80 mV, nisoldipine blocked I(Ba) of day 12.5 p.c. (+/+) and (+/-) cells with two IC(50) values of approximately 0.1 and approximately 1 microm. Inhibition of I(Ba) of (-/-) cardiomyocytes was monophasic with an IC(50) of approximately 1 microm. The low affinity I(Ba) was also present in cardiomyocytes of homozygous alpha(1D) (Ca(v)1.3) knockout embryos at day 12.5 p.c. These results indicate that, up to day 14 p.c., contraction of murine embryonic hearts requires an unidentified, low affinity L-type like calcium channel.
authors.affiliation: Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Strasse 29, D-80802 München, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Seisenberger
authors.forename: V
authors.initials: V
authors.lastname: Specht
authors.forename: A
authors.initials: A
authors.lastname: Welling
authors.forename: J
authors.initials: J
authors.lastname: Platzer
authors.forename: A
authors.initials: A
authors.lastname: Pfeifer
authors.forename: S
authors.initials: S
authors.lastname: Kühbandner
authors.forename: J
authors.initials: J
authors.lastname: Striessnig
authors.forename: N
authors.initials: N
authors.lastname: Klugbauer
authors.forename: R
authors.initials: R
authors.lastname: Feil
authors.forename: F
authors.initials: F
authors.lastname: Hofmann
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000235:genetics* / Q000502:physiology*; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005091:Exons; D005822:Genetic Vectors; D005838:Genotype; D006321:Heart / Q000196:embryology*; D006720:Homozygote; D020128:Inhibitory Concentration 50; D007477:Ions; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D008957:Models, Genetic; D009206:Myocardium / Q000166:cytology*; D015737:Nisoldipine / Q000494:pharmacology; D010641:Phenotype; D012313:RNA / Q000378:metabolism; D013997:Time Factors
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D018076:DNA, Complementary; D007477:Ions; C419385:L-type calcium channel alpha(1C); D001464:Barium; D015737:Nisoldipine; D012313:RNA; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester