title: Interaction between Ca(2+)  channel blockers and isoproterenol on L-type Ca(2+)  current in canine ventricular cardiomyocytes.
abstract: OBJECTIVE
  The aim of this work was to study antagonistic interactions between the effects of various types of Ca(2+)  channel blockers and isoproterenol on the amplitude of L-type Ca(2+)  current in canine ventricular cells.
  
  
  METHODS
  Whole-cell version of the patch clamp technique was used to study the effect of isoproterenol on Ca(2+)  current in the absence and presence of Ca(2+)  channel-blocking agents, including nifedipine, nisoldipine, diltiazem, verapamil, CoCl(2)  and MnCl(2) .
  
  
  RESULTS
  Five micromolar Nifedipine, 1 μM nisoldipine, 10 μM diltiazem, 5 μM verapamil, 3 mM CoCl(2)  and 5 mM MnCl(2)  evoked uniformly a 90-95% blockade of Ca(2+)  current in the absence of isoproterenol. Isoproterenol (100 nM) alone increased the amplitude of Ca(2+)  current from 6.8 ± 1.3 to 23.7 ± 2.2 pA/pF in a reversible manner. Isoproterenol caused a marked enhancement of Ca(2+)  current even in the presence of nifedipine, nisoldipine, diltiazem and verapamil, but not in the presence of CoCl(2)  or MnCl(2) .
  
  
  CONCLUSIONS
  The results indicate that the action of isoproterenol is different in the presence of organic and inorganic Ca(2+)  channel blockers. CoCl(2)  and MnCl(2)  were able to fully prevent the effect of isoproterenol on Ca(2+)  current, while the organic Ca(2+)  channel blockers failed to do so. This has to be born in mind when the effects of organic Ca(2+)  channel blockers are evaluated either experimentally or clinically under conditions of increased sympathetic tone.
authors.affiliation: Department of Dentistry, University of Debrecen, Debrecen, Hungary.
authors.forename: V
authors.initials: V
authors.lastname: Farkas
authors.forename: N
authors.initials: N
authors.lastname: Szentandrássy
authors.forename: L
authors.initials: L
authors.lastname: Bárándi
authors.forename: B
authors.initials: B
authors.lastname: Hegyi
authors.forename: F
authors.initials: F
authors.lastname: Ruzsnavszky
authors.forename: O
authors.initials: O
authors.lastname: Ruzsnavszky
authors.forename: B
authors.initials: B
authors.lastname: Horváth
authors.forename: T
authors.initials: T
authors.lastname: Bányász
authors.forename: J
authors.initials: J
authors.lastname: Magyar
authors.forename: I
authors.initials: I
authors.lastname: Márton
authors.forename: P P
authors.initials: PP
authors.lastname: Nánási
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002478:Cells, Cultured; D004285:Dogs; D004347:Drug Interactions; D005260:Female; D006352:Heart Ventricles / Q000166:cytology*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects*
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D007545:Isoproterenol; D002118:Calcium