Faculty Bibliography

1. Ganglion cell discharges were evoked by extrinsic polarization of the horizontal cells in the retina of the smooth dogfish (Mustelus canis). Depolarization of the horizontal cell gave rise to a discharge similar to that evoked by a spot of light (centre type response) and hyperpolarization of the horizontal cell, a discharge similar to that by an annulus (surround type response).2. Procion dye injection established that the current-passing electrode was sometimes located in the external horizontal cell. Other possibilities, such as middle and internal horizontal cells, were neither confirmed nor excluded.3. Activation of ganglion cells by current was possible under completely dark-adapted conditions and for several log units above this level.4. Depolarizing current enhanced the ganglion cell response evoked by a light spot in the centre of its receptive field; hyperpolarizing current antagonized the response to the same flash.5. The results are consistent with the supposition that a potential change in the horizontal cell, irrespective of its polarity, or whether produced by light or current, spreads within a laminar layer (the S-space). The effect of the potential change is to modulate the response of bipolar cells and their input into the ganglion cell.

1. The influence of diastolic interval on ionic currents that may determine the action potential duration in cardiac Purkinje fibres was investigated. As the diastolic interval is shortened from about 5 sec, the first effect on the action potential is to reduce and then abolish the notch at the beginning of the plateau.2. This effect corresponds to the influence of diastolic interval on the magnitude of a transient outward chloride current known as the ;dynamic current'.3. Further shortening of the diastolic interval produces a slight shortening of the action potential until intervals less than about 500 msec are used. The action potential then becomes considerably shorter. The ;time constant' of decay of this major influence of one action potential on the duration of the subsequent action potential is about 200 msec.4. This effect corresponds to the time course of decay of an outward (mainly K) current known as i(x1).5. It is shown that variations in the magnitude of i(x1) may be responsible for the alternation in action potential duration at the beginning of a train of stimuli known as ;electrical alternans'.6. The results in general are consistent with the view that i(x1) is the main current involved in determining the interval-duration relation although they cannot exclude the possibility that an inward current with a reavailability time course similar to the decay time course of i(x1) might also be involved