title: Manganese-dependent propagated action potentials and their depression by electrical stimulation in guinea-pig myocardium perfused by sodium-free media.
abstract: 1. Propagated action potentials were recorded in right ventricular papillary muscles from guinea-pig heart while exposed to Na-free, Ca-free and Mg-free solutions containing Mn. 2. When Na was totally replaced by 95 mM-Mn the overshoot was about 45 mV while the resting potential was about -90mV. 3. The overshoot of action potentials was increased by about 20-30 mV per tenfold increase of Mn concentration over the range of 2-50 mM. 4. Similar increases of overshoots with increasing of Mn concentration also occurred in the presence of 0-6 mM-Ca. Increasing of Ca from 5 to 20 mM had little influence on the overshoot but shortened the duration of the Mn-dependent action potential in the presence of 5 mM-MN. 5 Mn-dependent action potentials were not depressed by 3 X 10(5) M tetrodotoxin but by La. 6. These results suggest that Mn passes through the slow inward current channel to generate the action potential seen under the Na-free condition. 7. The overshoot and duration of the Mn-dependent action potential decreased with stimulation. At stimulus frequencies (Hz) of 0-5, 0-2, 0-1, 0-017 and 0-0033 the overshoot of action potential in 5 mM-Mn Tyrode decreased by 0-5-1 mV per an action potential.  This depression of the action potential is explained by assuming intracellular accumulation of Mn.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D010210:Papillary Muscles / Q000187:drug effects* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D008345:Manganese; D013779:Tetrodotoxin; D007811:Lanthanum; D002118:Calcium