H. Stieve et al., THE EFFECTS OF EXTERNALLY APPLIED LITHIUM AND STRONTIUM ON THE ARSENATE-MONITORED CYTOSOLIC CALCIUM SIGNAL OF THE LIMULUS VENTRAL PHOTORECEPTOR, Zeitschrift fur Naturforschung. C, A journal of biosciences, 49(5-6), 1994, pp. 372-392
The intracellular arsenate signal indicating the transient light-evoke
d change in cytosolic Ca2+ (or Sr2+) concentration was measured in Lim
ulus ventral photoreceptor simultaneously with the receptor potential
at 15 degrees C. The decline of the arsenate signal has two phases (D1
and D2) when the photoreceptor is bathed in physiological saline. 1.
When calcium is replaced by strontium in the superfusate both receptor
potential and arsenate signal are markedly increased in amplitude and
the membrane potential is hyperpolarized. The decline of the arsenate
signal is prolonged and becomes monophasic; the fast phase D1 of the
decline disappears. 2. In strontium saline under voltage clamp conditi
ons the slope of the monophasic decline of the arsenate signal is the
steeper the more negative the membrane voltage. 3. After replacing sod
ium by lithium in the superfusate the rise of the receptor potential a
nd of the arsenate signal are not much altered. The decline of the ars
enate signal, however, is slowed down more than 3-fold; this is due to
the complete suppression of the fast phase D1 and the retardation of
the slow phase D2 of the calcium re-decline.