The correlation of the receptor potential with the light induced transient increase in intracellular calcium-concentration measured by absorption change of arsenazo III injected into Limulus ventral nerve photoreceptor cell

Abstract

The light-induced membrane voltage response (receptor potential, ReP) and the absorption change of the intracellularly injected calcium indicator arsenazo III (arsenazo response) were recorded simultaneously in Limulus ventral nerve photoreceptor cells. A double pulse technique was applied for stimulation. After pressure injection of the indicator into the cell absorption changes were measured at 646 nm to obtain a measure of the changes of the intracellular calcium ion concentration. 1. The size of the arsenazo response increases with increasing intensity of the light stimulus. The intensity dependence of the size of the arsenazo response delta A max shows almost no correlate with the peak amplitude of the ReP, but correlates rather well with the time integral of the ReP. 2. Decreasing light adaptation (caused by prolongation of the repetition time of the pulse pairs) leads to an increase in size of the arsenazo response. Also here delta A max correlates better with the time integral of the ReP than with its peak amplitude. 3. Lowering the calcium concentration in the superfusate (from 10 mmol/l to ca. 40 mumol/l) causes after ca. 10 min a drastical diminution of the arsenazo response to values below the noise level, and a less marked reduction in size of the ReP. The falling phase of the ReP is slower. After return to normal calcium concentration the arsenazo response recovers partly in ca. 50 min, while the ReP recovers faster. The results show two opposite correlation between ReP and arsenazo response: Increase in size and duration of the ReP causes a greater transient increase of the intracellular calcium ion concentration. This in turn tends to reduce and shorten the ReP. Which effect dominates obviously depends on the conditions of the experiment: when the calcium concentration in the superfusate is reduced to ca. 40 mumol/l a slow decrease of the ReP is accompanied by a small increase of the intracellular calcium ion concentration.

Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.

“…Effect of Light Adaptation on the Light-induced Ca ; Increase J. E. Brown and Blinks (1974), using aequorin, and Maaz and Stieve (1980), using arsenazo 111, showed that the amplitude of the indicator response was related to the adaptational state of the cell . In those experiments, the state of adaptation was varied by changing the interstimulus interval for a pair of equally bright stimuli: the aequorin or the arsenazo signal elicited by the second stimulus of the pair became smaller as the interstimulus interval decreased.…”

“…Beyond this question, a controversy exists regarding the source of the Ca ions that gives rise to the light-induced Ca ; increase (J . E. Brown and Blinks, 1974 ;Lisman, 1976 ;Maaz and Stieve, 1980) . Here we present evidence that bathing the photoreceptors in low Ca.…”

Ca2+-sequestering smooth endoplasmic reticulum in an invertebrate photoreceptor. II. Its properties as revealed by microphotometric measurements.

“…Less elaborate, but also well developed, are Ca2+-sequestering sub-surface cisternae associated with the nonreceptive plasma membrane areas of the cell (43) . These two prominent high-affinity Ca"-buffering SER elements thus possess a strategic position relative to the cell periphery where stimulus-induced changes of Cai+ (6,8,9,26) most probably take place.…”

“…The Ca pump has a high affinity for Ca 2+ ions : the threshold for activation of the pump is -5 X 10 -8 M, the apparent KM,c,, is -4 X 10 -7 M . When Na' or Li + is substituted for K+ , Ca uptake rate is decreased by 40-50% .The results show that the Ca t+ -sequestering SER in leech photoreceptors shares some basic properties with skeletal muscle sarcoplasmic reticulum and supports the idea that certain subregions of the SER in invertebrate photoreceptors function as effective Ca 2+ sinks/buffers close to the plasmalemma.Direct evidence from measurements with Ca 2+ indicators (6,8,9,26) and Ca'-sensitive microelectrodes (6), as well as indirect evidence from electrophysiological experiments (see, for example, references 1,15,24,25,35), suggest that the free calcium concentration (Caû,+) in the cytosol of photoreceptor cells of invertebrates increases upon illumination. Several laboratories have shown that this light-induced increase of Cap' modulates the adaptational state of the cells (see reference 7 for review), a Cat+-dependent potassium conductance (see, for example, reference 17, 18, 38), and mediates the light-induced pigment granule migration in fly photoreceptors (22) .…”

“…Direct evidence from measurements with Ca 2+ indicators (6,8,9,26) and Ca'-sensitive microelectrodes (6), as well as indirect evidence from electrophysiological experiments (see, for example, references 1,15,24,25,35), suggest that the free calcium concentration (Caû,+) in the cytosol of photoreceptor cells of invertebrates increases upon illumination. Several laboratories have shown that this light-induced increase of Cap' modulates the adaptational state of the cells (see reference 7 for review), a Cat+-dependent potassium conductance (see, for example, reference 17,18,38), and mediates the light-induced pigment granule migration in fly photoreceptors (22) .…”