title: Possible existence of transient TTX-sensitive chloride current in the membrane of isolated cardiomyocytes.
abstract: Cardiomyocytes enzymatically isolated from rat and guinea pig ventricular tissue were investigated under conditions of intracellular perfusion and voltage clamp at 18-20 degrees C. Perfusion with 135 mmol/l Tris(HF), pH 7.2 was used to eliminate outward potassium currents. The dependence of inward current (elicited by depolarizing pulses from a holding potential level of--120 mV) on low external TTX concentrations (from 10(-13) to 10(-10) mol/l) was studied. Similar TTX concentrations increased the amplitude of the inward current and changed its kinetics in a large number of cells tested. The effect was fully reversible. The effect could be evaluated in a net form by digital subtraction of the current obtained after the application of a low external TTX concentration from the initial current in a TTX-free solution. The TTX concentration dependence of the difference current could be fitted by one-to-one binding curve with Kd = (1.0 +/= 0.4) x 10(-12) mol/l. TTX-induced current changes were absent in low sodium or chloride-free external solutions. The outward current (a block of which by TTX produced the inward current changes observed) showed a reversal potential consistent with the chloride nature of such a current. The existence of a transient TTX-sensitive Na-dependent potential gated chloride current in the membrane of isolated cardiomyocytes is postulated.
mesh_terms: D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D013779:Tetrodotoxin / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D007473:Ion Channels; D013779:Tetrodotoxin