title: The effects of manganese and barium on the cardiac pacemaker current, if, in rabbit sino-atrial node myocytes.
abstract: The isolation of ionic fluxes contributing to electric currents through cell membranes often requires block of other undesired components which can be achieved, among others, by divalent cations. Mn2+ and Ba2+ are often used, for example, to block Ca and K currents. Here we have investigated the effects of these two cations on the properties of the hyperpolarization-activated pacemaker current if, in rabbit sino-atrial node myocytes, as obtained by voltage clamp analysis. We find that 2 mM Mn2+ shifts the if activation curve by 3.2 +/- 0.3 mV towards more positive values. However, when 1 mM Ba2+ is also added, the positive shift is more than halved (1.3 +/- 0.2 mV). We find, too, that in the absence of blocking cations the ACh-induced if inhibition is slightly higher than in their presence. These results indicate that the alteration of if kinetic properties by Ba2+ plus Mn(2+)-containing solutions is minimal.
authors.affiliation: Dipartimento di Fisiologia e Biochimica Generali, Milano, Italy.
authors.forename: D
authors.initials: D
authors.lastname: DiFrancesco
authors.forename: F
authors.initials: F
authors.lastname: Porciatti
authors.forename: I S
authors.initials: IS
authors.lastname: Cohen
mesh_terms: D000109:Acetylcholine / Q000008:administration & dosage; D000818:Animals; D001464:Barium / Q000008:administration & dosage / Q000494:pharmacology*; D001711:Biotransformation; D004305:Dose-Response Relationship, Drug; D008345:Manganese / Q000008:administration & dosage / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology; D010138:Pacemaker, Artificial; D011817:Rabbits; D012849:Sinoatrial Node / Q000187:drug effects*
chemical_list: D001464:Barium; D008345:Manganese; D000109:Acetylcholine