Faculty Bibliography

1. Experiments on sheep Purkinje fibres were designed to determine whether the current mechanisms responsible for delayed rectification at the pace-maker (negative to -50 mV) and plateau (positive to -50 mV) ranges of potential are kinetically separable and independent.2. Hyperpolarizations from the plateau range were shown to produce decay of a single component of outward current within the plateau range, but two components were evident when the hyperpolarizations entered the pace-maker range.3. The time courses of recovery of the two components were too similar at -25 mV to allow temporal resolution at this potential. Clear temporal resolution was, however, possible at potentials between -55 and -95 mV. An indirect method of resolving the two components at -25 mV was used.4. The kinetic properties of the two components correspond to those previously described for the pace-maker potassium current, i(K) (2), and the outward plateau current, i(x) (1) (Noble & Tsien, 1968, 1969a).5. The instantaneous (fully activated) current-voltage relation for i(K) (2) was reconstructed from the analysed current records. It was found that this relation shows a negative slope conductance at all potentials positive to -75 mV and that the current tends towards zero at zero membrane potential.6. The results are compared with those predicted by two reaction models of the i(K) (2) and i(x) (1) mechanisms. It is concluded that i(K) (2) and i(x) (1) are kinetically separable but that it is not possible with present techniques to decide whether they are controlled by the same or completely independent membrane structures. It is also shown that the instantaneous current-voltage relation calculated for i(K) (2) does not depend on whether the controlling mechanisms are assumed to be independent or linked

Dopamine-beta-hydroxylase activity is present in mouse neuroblastoma C-1300 tumors. The activity is proportional to the weight of the tumor. Serum activity is markedly increased in mice that bear the tumors. Treatment of mice with 5-bromodeoxyuridine causes marked inhibition of tumor growth and decrease of dopamine-beta-hydroxylase activity in the serum. The histochemical studies reveal that 1-5% of the cells in mouse C-1300 neuroblastoma tumors contain catecholamines and that catecholamine-containing processes terminate mainly around blood vessels of the tumor. Dopamine-beta-hydroxylase is present in clonal neuroblastoma cell lines. The cell line with the greater tendency to form axon-like processes has a higher activity of this enzyme