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Continuum of type λDendrite Hilbert cube Induced map Topological entropy Transitivity For a metric continuum X, we consider the hyperspaces 2 X and C (X) of the closed and nonempty subsets of X and of subcontinua of X, respectively, both with the Hausdorff metric. For a given map f : X → X we investigate the transitivity of the induced maps 2 f : 2 X → 2 X and C ( f ) : C (X) → C (X). Among other results, we show that if X is a dendrite or a continuum of type λ and f : X → X is a map, then C ( f ) is not transitive. However, if X is the Hilbert cube, then there exists a transitive map f : X → X such that 2 f and C ( f ) are transitive.

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Measurements of the K activity (aiK) in ferret ventricle were made using either single‐ or double‐barrelled K‐sensitive micro‐electrodes. aiK was also estimated from the Nernst equation by measuring the membrane potential when changing the external K concentration. Microelectrodes filled with the Corning K sensor gave unreliable results most probably due to interference from some substance(s) in the heart cells. Reproduceable measurements were obtained using a valinomycin cocktail as the K sensor. The mean value ± S.D. for aiK from four experiments which met strict criteria for calibration, electrode penetration and drift was 104 mmol/l ± 9 mmol/l. If all nine experiments were taken the value was 101 mmol/l ± 8 mmol/l. Estimation from the Nernst equation gave values of aiK that were on average 20 mmol/l higher than the measured values with the valinomycin cocktail. It is recommended that a valinomycin cocktail be used to measure aiK.