Measurement of intracellular 42K diffusion in frog ventricular strips.

The longitudinal distribution of 42K was measured in strips of frog ventricular muscle placed in a partitioned perfusion chamber. A radiation detector placed directly under the chamber was moved from point to point to scan the longitudinal distribution of 42K. The detector was focussed on a 0.6 mm segment of the strip by means of two slits and two Geiger tubes. A beta-particle from the strip was counted only if it passed through both Geiger tubes. This arrangement improved the spatial resolution and decreased the background and the sensitivity to Compton electrons. The intracellular diffusion constant measured with this system is 3.7 X 10(-6) cm2/s.