title: Inhibition by magnesium of calcium inward current in heart ventricular muscle.
abstract: It was investigated whether the negative inotropic effect of magnesium in mammalian heart ventricular muscle is due to inhibition of the calcium inward current. Whole-cell voltage-clamp experiments were carried out with isolated guinea-pig heart cells. The sodium inward current was inactivated by a conditioning pre-pulse or by addition of tetrodotoxin. Magnesium concentration dependently and reversibly diminished the calcium inward current (by about 45% after an increase in magnesium concentration, from 1.2 to 9.6 mM). The decrease was mainly due to diminution of the maximally available calcium inward current but was additionally due to a shift of the current-voltage relationship to more positive potentials. The crucial dependence of the inhibition of the inward current on the pre-pulse potential was demonstrated. Conditioning depolarization to potentials more negative than -40 mV led to an increase of an inward current by magnesium. This was probably the consequence of incomplete inactivation of the sodium current and the shift of its current-voltage relationship by the divalent cation.
authors.affiliation: Institut für Pharmakologie und Toxikologie, Technischen Universität München, F.R.G.
authors.forename: A
authors.initials: A
authors.lastname: Dichtl
authors.forename: W
authors.initials: W
authors.lastname: Vierling
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006325:Heart Atria; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D008274:Magnesium; D002118:Calcium; D009638:Norepinephrine