Potassium Efflux from Amphibian Atrium during the Cardiac Cycle: A REEXAMINATION
Fine fibers from amphibian atrium were mounted in a microperfusion chamber and loaded with 42K, followed by a rapid, nonisotopic wash during which the preparation was stimulated electrically. The stimulus was triggered and the "cold" effluent collected by a high-speed rotary fraction collector. Thus effluent corresponding to the same time interval in the cardiac cycle was always collected in the same tube. Large numbers of cycles were thus summed, decreasing the error in the tracer assay. Mechanical systole, previously shown to produce an artifact in the tracer efflux profile, was suppressed or prevented by various means. Under these conditions, a prolonged decrease in 42K efflux was observed, corresponding in time to the plateau of the action potential. Experiments were also carried out with 22Na, 45Ca, and 82Br, all of which showed primarily a single, positive efflux peak with its maximum within the first 50 msec of the action potential. Cell membrane permeability to K+ appears to be markedly voltage dependent; and a diminished membrane permeability to K+ apparently plays an important part in the generation of the plateau of the cardiac action potential.
- 22Na, 45Ca, and 82Br efflux from frog heart
- cardiac permeability to K+
- K+ and cardiac membrane potential
- Ni2+, zero Ca2+ and plateau of heart action potential
- Received November 4, 1971.
- Accepted January 7, 1972.
- © 1972 American Heart Association, Inc.