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Atrial and ventricular myocytes were exposed to Ca(2+)- and K(+)-free solutions containing blockers of gated channel and exchange currents. Replacement of external sodium by large organic cations revealed a background sodium current ib,Na. In atrial cells, the average conductance was 5.0 pS pF-1. In ventricular cells the conductance was 2.3 pS pF-1.(More)
1. A double sucrose gap method has been used to polarize and voltage clamp frog atrial muscle strips.2. In response to steady depolarizing currents, normally quiescent strips often show pace-maker activity, and long lasting depolarization occurs when the current is terminated.3. Voltage clamp experiments reveal the presence of two current components(More)
1. Slow inward tail currents attributable to electrogenic sodium-calcium exchange can be recorded by imposing hyperpolarizing voltage clamp pulses during the normal action potential of isolated guinea-pig ventricular cells. The hyperpolarizations return the membrane to the resting potential (between -65 and -88 m V) allowing an inward current to be(More)
1. The spontaneous electrical activity of small strips of muscle from the sinus venosus region of the heart of Rana catesbeiana was investigated using the double sucrose gap technique. The voltage clamp was used to record the ionic currents underlying the pace-maker depolarization and the action potential.2. The records of spontaneous electrical activity(More)
1. A method is described for determining the space constant gamma of heart muscle strips using a sucrose gap technique. 2. The average value of gamma for frog atrial trabeculae was found to be nearly 700 mum. This value is nearly twice the length of the test gap (400 mum). Near the resting potential, the voltage non-uniformity should be about 10%. This was(More)
1. A quantitative analysis of the time-dependent component of outward membrane current in atrial wall trabeculae from Rana catesbeiana and Rana ridibunda has been carried out using a double sucrose gap technique. 2. Separation of the different components of delayed outward current was hampered by the sigmoid onset of one of the outward current systems(More)
DiFrancesco & Noble's (1984) equations (Phil. Trans. R. Soc. Lond. B (in the press.] have been modified to apply to the mammalian sino-atrial node. The modifications are based on recent experimental work. The modified equations successfully reproduce action potential and pacemaker activity in the node. Slightly different versions have been developed for(More)
1. The nature and interactions of the membrane currents underlying induced pace-maker activity in frog atrial muscle have been investigated using a double sucrose gap technique. 2. The membrane current which controls the speed of the atrial pacemaker depolarization (the pace-maker current, ip), is shown to be an outward current activated within the plateau(More)