title: Protein kinase G reverses all isoproterenol induced changes of cardiac single L-type calcium channel gating.
abstract: OBJECTIVE
  cGMP reduces the effect of beta-adrenoceptor agonists on cardiac L-type calcium current by protein kinase G activation. Stimulation of beta-adrenoceptors increases protein kinase A dependent phosphorylation of L-type calcium channels via cAMP. At the single channel level, protein kinase A dependent phosphorylation increases both availability and open probability. The present study investigates how cGMP antagonises protein kinase A induced changes of single L-type calcium channel gating.
  
  
  METHODS
  Single L-type calcium channels were recorded in the cell attached configuration of the patch clamp technique in isolated mouse ventricular myocytes.
  
  
  RESULTS
  The beta-adrenoceptor agonist isoproterenol (10(-6) M) enhanced single channel peak average current by increasing availability and open probability and decreasing the time constant of long close times. 8-Br-cGMP (10(-3) M) completely reversed these effects. The phosphatase inhibitor okadaic acid (10(-6) M) did not influence the effect of 8-Br-cGMP. The protein kinase G inhibitor Rp-8Br-PET-cGMPS (10(-7) M) abated the effect of 8-Br-cGMP. Activation of protein kinase A by the hydrolysis-resistant cAMP derivative 8-Br-cAMP (10(-3) M) enhanced L-type calcium channel activity like isoproterenol and its effect was also reversed by 8-Br-cGMP.
  
  
  CONCLUSIONS
  8-Br cGMP diminishes beta-adrenoceptor activation of L-type calcium channels via protein kinase G. It interacts with the beta-adrenoceptor signaling pathway distal of adenylyl cyclase. Our observations suggest that protein kinase G interacts either with protein kinase A or directly with the L-type calcium channel.
authors.affiliation: Department of Cardiology and Angiology, Hannover Medical School, Carl-Neuberg-Strasse 1, D-30625, Hannover, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Klein
authors.forename: H
authors.initials: H
authors.lastname: Drexler
authors.forename: F
authors.initials: F
authors.lastname: Schröder
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D051379:Mice; D009206:Myocardium / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D015290:Second Messenger Systems / Q000502:physiology*
chemical_list: D000318:Adrenergic beta-Agonists; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D019319:Okadaic Acid; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016276:8-bromocyclic GMP; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D010744:Phosphoric Monoester Hydrolases; D006152:Cyclic GMP; D007545:Isoproterenol