Light-initiated currents in Limulus lateral eye retinular cells were studied using the voltage clamp technique. To assess the validity of such current measurements, the isopotentiality of retinular cells was determined on triply impaled cells and the effect of voltage clamping one retinular cell on adjacent retinular cells and on the eccentric cell in the same ommatidium was determined. The results of the experiments are: (1) retinular cells are isopotential at loci 100 micron apart; (2) appreciable steady state current during the clamping episodes leaks into neighboring retinular cells and the eccentric cell; (3) light-initiated currents exhibit two components; (4) there is a dynamic change in the resistance of the photoreceptor membrane during development of the receptor potential; (5) suppression of the rising phase (C1) of the receptor potential does not affect subsequent voltage changes; (6) suppression of the sodium influx which normally produces C1 has only minor effects on subsequent voltage changes; (7) reduced [KC1]out increases and increased [CK1]out decreases the reversal potential of light-initiated currents; and (8) reduced [NaC1]out reduces the magnitude and the reversal potential of light-initiated currents.

Animals↗

PubMedDate not supplied

Partial voltage clamping of Limulus ventral photoreceptor potentials: evidence of programmed conductance changes.

Light-initiated currents elicited by brief light stimuli from Limulus ventral photoreceptors bathed in normal sea water generally exhibit a smooth contour, although the unclamped receptor potential elicited by an identical light stimulus usually exhibits distinct C1 and C2 components. However, light-initiated currents obtained from cells exposed to chlorobutanol often exhibit two components. Data from such experiments indicate that peak C2 current is more strongly voltage dependent than peak C1 current, as in Limulus lateral eye retinular cells. The results of partial voltage clamp experiments with ventral photoreceptors in which the clamping episode terminated at different times during the receptor potential reveal relatively minor perturbations of the rebound receptor potential when compared with the unclamped control response. These findings suggest that the temporal pattern of the membrane conductance changes which underlie the receptor potential is determined prior to the occurrence of the receptor potential. It is likely that the program for these conductance changes is developed during the latent period of the receptor potential.

Animals↗

PubMedDate not supplied

Egg shell formation and bone resorption in laying hens.

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Acid-Base Equilibrium↗