Voltage clamp analysis of embryonic heart cell aggregates.
The double-microelectrode voltage clamp technique was applied to small spheroidal aggregates of heart cells from 7-d chick embryos. A third intracellular electrode was sometimes used to monitor spatial homogeneity. On average, aggregates were found to deviate from isopotentiality by 12% during the first 3--5 ms of large depolarizing voltage steps, when inward current was maximal, and by less than 3% thereafter. Two components of inward current were recorded: (a) a fast, transient current associated with the rapid upstroke of the action potential, which was abolished by tetrodotoxin (TTX); and (b) a slower inward current related to the plateau, which was not affected by TTX but was blocked by D600. The magnitudes, kinetics, and voltage dependence of these two inward currents and a delayed outward current were similar to those reported for adult cardiac preparations. From a holding potential of -60 mV, the peak fast component at the point of maximal activation (-20 mV) was -185 microA/cm2. This value was about seven times greater than the maximal slow component which peaked at 0 mV. The ratio of rate constants for the decay of the two currents was between 10:1 and 30:1.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology*
D013779:Tetrodotoxin