G. Stommel et al., THE LIGHT-STIMULATED CYTOSOLIC CALCIUM TRANSIENT IN LIMULUS VENTRAL NERVE PHOTORECEPTORS - 2 COMPONENTS IN THE RISING PHASE, Zeitschrift fur Naturforschung. C, A journal of biosciences, 51(1-2), 1996, pp. 101-112
1. Light-evoked electrical responses were measured in Limulus ventral
nerve photoreceptors simultaneously with changes in the cytosolic free
calcium concentration, by means of arsenate III. 2. It has been shown
here for the first time that the rise of the arsenate signal consists
of two phases. Only the slow phase in the rise of the signal depends
on the membrane voltage. The reversal potential of the amplitude of th
is slow rising phase was about +196 mV. After removal of external calc
ium the reversal potential was about +20 mV. 3. When Na+ in the superf
usate was replaced by Li+, the amplitude of the fast rising phase was
reduced on the average to 50%, while the slow rising phase was not aff
ected. 4. We conclude that the fast rising phase is caused by release
of calcium from internal stores while the slow increase in [Ca2+](i) i
s due to influx across the plasma membrane, possibly through light-act
ivated ion channels.