Abstract
We previously showed that stimulation of cGMP-dependent protein kinase (PKG) stimulates L-type calcium current in newborn but not in adult rabbit ventricular myocytes. We have now isolated rabbit PKG type Iα cDNA (+1 to 2095), determined the sequence, and analyzed specific expression of PKG in adult and newborn rabbit heart by Western and Northern analyses to elucidate the developmental decline in the significance of PKG in cardiac function. We obtained full-length cDNA of PKG Iα from newborn rabbit heart mRNA with reverse transcription-polymerase chain reaction. The coding region of rabbit PKG Iα showed 94% homology to sequences of human and bovine PKG Iα. The deduced amino acid sequence of 671 amino acids showed seven substitutions between rabbit and either human or bovine PKG Iα. The major substitutions were found in the cGMP-binding domain. The cloned PKG 1α cDNA was expressed in COS cells. Expressed PKG showed cGMP stimulated PKG activity and immunoreactivity. Northern blot analysis of cardiac tissue demonstrated PKG Iα mRNA of 6.8 kb, with much higher levels in newborn than in adult cells. Western analysis in homogenates from ventricular tissues and isolated ventricular myocytes of rabbit heart showed much higher expression of PKG type I protein in newborn compared with adult cells. These findings suggest that PKG is developmentally regulated in rabbit heart and is expressed at a much higher level in newborn than in adult cells. The greater expression of PKG in newborn cells could be responsible for differences in the significance of cGMP in adult and newborn rabbit cells.
Footnotes
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Send reprint requests to: Dr. Rajiv Kumar, Ph.D., Department of Pediatrics, Emory University School of Medicine, 2040 Ridgewood Dr. NE, Atlanta, GA 30322. E-mail:Rajiv{at}cellbio.emory.edu
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↵1 This work was partially supported by a grant-in-aid from American Heart Association (to R.K.), National Institutes of Health Grants HL56787 (to R.K.) and HL49438 (to R.W.J.), The Children's Heart Center, and by the Emory Egleston Children's Research Center.
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↵2 Current address: Department of Pathology, Division of Molecular and Cellular Pathology, University of Alabama at Birmingham, Volker Hall, 1670 University Blvd., Birmingham, AL 35294.
- Abbreviations:
- PKG
- cGMP-dependent protein kinase
- PDE
- phosphodiesterase
- IBMX
- 3-isobutyl-1-methylxanthine
- TBS
- Tris-buffered saline
- PCR
- polymerase chain reaction
- RT
- reverse transcription
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- NB
- newborn
- AD
- adult
- ICa
- L-type calcium current
- Received November 24, 1998.
- Accepted August 12, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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