title: Effects of cGMP on L-type calcium current of adult and newborn rabbit ventricular cells.
abstract: OBJECTIVE
  Cyclic GMP has been shown to be in some respects an inhibitory modulator of heart function. Various studies on the modulation of cardiac L-type calcium current (ICa) by cGMP in different species show inconsistency and the role of cGMP remains unclear and controversial. The present study was focused on the differences in the modulation of basal ICa by cGMP in adult and newborn rabbit ventricular cells.
  
  
  METHODS
  Enzymatically isolated adult and newborn (1-4-day-old) rabbit ventricular myocytes were used to measure ICa under whole-cell voltage clamp conditions with internal perfusion of isolated cells.
  
  
  RESULTS
  We have shown that in adult ventricular cells, the intracellular perfusion of 8BrcGMP did not produce any effect on basal ICa, while intracellular perfusion of 8BrcGMP or 8CPT-cGMP in newborn ventricular cells significantly and reversibly increased basal ICa without changing the voltage dependence for activation of ICa. Both methylene blue and LY-83583 (which inhibit guanylyl cyclase and thus lower cGMP levels), in adult ventricular cells, failed to produce any significant effect on basal ICa, while in newborn ventricular cells the application of methylene blue or LY-83583 produced irreversible inhibition of basal ICa. Similarly, KT-5823, an inhibitor of cGMP-dependent protein kinase, also inhibited basal ICa in newborn ventricular cells but not in adult ventricular cells. However, extracellular application of methylene blue during the intracellular perfusion of 8BrcGMP was unable to inhibit ICa. Extracellular application of nitrosoglutathione which releases nitric oxide produced a significant increase in ICa in newborn but not in adult ventricular cells. Intracellular application of a cAMP-dependent protein kinase inhibitor peptide blocked the stimulatory effect of cAMP but not of 8CPT-cGMP, while the stimulatory effect of nitrosoglutathione on ICa was not blocked by the presence of a phosphodiesterase inhibitor (isobutylmethyl-xanthine).
  
  
  CONCLUSIONS
  We propose that, for newborn rabbit ventricular cells, cGMP plays a crucial role in maintaining basal ICa by a mechanism mediated via protein-kinase-G-dependent phosphorylation of calcium channels or some associated protein.
authors.affiliation: Todd Franklin Cardiac Research Laboratory, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: R
authors.initials: R
authors.lastname: Kumar
authors.forename: T
authors.initials: T
authors.lastname: Namiki
authors.forename: R W
authors.initials: RW
authors.lastname: Joyner
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000470:Alkaloids / Q000494:pharmacology; D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects*; D002227:Carbazoles; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D005260:Female; D005978:Glutathione / Q000031:analogs & derivatives / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D007211:Indoles; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D009603:Nitroso Compounds / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D011817:Rabbits; D026422:S-Nitrosoglutathione; D013873:Thionucleotides / Q000494:pharmacology; D013997:Time Factors
chemical_list: C090860:8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphorothioate; D000470:Alkaloids; D000634:Aminoquinolines; D015220:Calcium Channels; D002227:Carbazoles; D007211:Indoles; D009603:Nitroso Compounds; D010726:Phosphodiesterase Inhibitors; D047428:Protein Kinase Inhibitors; D013873:Thionucleotides; C073601:KT 5823; C016276:8-bromocyclic GMP; D026422:S-Nitrosoglutathione; C041715:6-anilino-5,8-quinolinedione; D017869:Cyclic GMP-Dependent Protein Kinases; D006162:Guanylate Cyclase; D005978:Glutathione; D006152:Cyclic GMP; D002118:Calcium; D008751:Methylene Blue; D015056:1-Methyl-3-isobutylxanthine