title: [Preliminary studies of the mechanism of carbachol increase contraction in rat ventricular myocytes].
abstract: OBJECTIVE
  To study whether the mAchR agonist Carbachol(Cch, nonselective) causes increased contractions and L-type Ca2+ current [L(Ca(L))] in ventricular myocytes and the mechanism of these effects.
  
  
  METHODS
  The effect of Cch on the I(Ca(L)) and Na/Ca exchange current (I(Na/Ca) was studied in patch-clamped ventricular myocytes isolated from rat hearts and superfused with Tyrode's solution (35 degrees C, 1.8 mmol/L [Ca2+]o) and stimulated at 0.2 Hz and 1.0 Hz evoke contractions of single myocyte.
  
  
  RESULTS
  (1) An increase of stimulation frequency decreased the contractions of myocytes(negative inotropic effects). (2) 100 micromol/L Cch increased contraction in 6 cells by 28% (delta L0.2 Hz/ delta L1.0 Hz > or = 1.25) at 1.0 Hz stimulus frequency. (3) The mAchR antagonist Atropine prevented the Cch effect. The mAchR agonist McN-A-343 (M1-selective) did not change the contractions in most of the cells. (4) 100 micromol/L Cch had no significant effect on basal I(Ca(L)), but increased the tail current density on repolarization from +10 mV to -40 mV, suggested that Cch increased I(Na/Ca).
  
  
  CONCLUSIONS
  The increase of cell contractions by Cch is apparently mediated by M2 mAchR and eventually increased I(Na/Ca). The increase Ca2+ content of the SR is reflected by the greater magnitude of I(Na/Ca). These results provide an explanation for the increased contraction of the rat ventricular myocytes by Cch and without changes in I(Ca(L)).
authors.affiliation: Department of Cardiology, First Affiliated Hospital of Suzhou University, Suzhou 215006, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Jiang
authors.forename: Zhi-hua
authors.initials: ZH
authors.lastname: Liu
authors.forename: A J
authors.initials: AJ
authors.lastname: Pappano
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology*; D018679:Cholinergic Agonists / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology*; D009119:Muscle Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000502:physiology
chemical_list: D020746:Calcium Channels, L-Type; D018679:Cholinergic Agonists; D019831:Sodium-Calcium Exchanger; D002217:Carbachol