Localized adaptation within the rhabdomeral lobe of Limulus ventral photoreceptors
نویسندگان
چکیده
Recent papers published in this journal (Stern et al., 1983; Calman and Chamberlain, 1983) have modified our understanding of the structure of Limulus ventral photoreceptors. The receptor's light-sensitive rhabdom has been found to be restricted to one or more specialized lobes termed R (rhabdomeral) lobes. In the light microscope, the R lobes can be distinguished from the A (arhabdomeral) lobe only after glial tissue has been removed from around the photoreceptor (Stern et al., 1983). Following these discoveries, previous studies of photoreception by the ventral eye may require revision. In particular, Stern et al. (1983) discuss the work of Fein and Charlton (1975) in which adaptat ion of the photoreceptor was shown to be localized within the cell. In this work, two spots of light were focused onto a cell having intact glia. Prolonged stimulation at one spot did not adapt the response to the other spot when the spots were separated by >50 #m. Stern et al. point out that the two spots may have been placed in separate R lobes within the same cell. This possibility leaves unresolved the question of whether adaptat ion is localized within a single R lobe. We have therefore repeated Fein and Charlton's (1975) experiment, using cells stripped of their glia so that the R lobes were clearly visible (Stern et al., 1983). After the glia and connective tissue had been removed from a ventral photoreceptor cell body (Stern et al., 1983), the axon remained the only part of the cell still a t tached to the ventral nerve. The free-floating cell body was held in place for intracellular recording by the use of a suction electrode (see Fig. 1A). The cell shown in Fig. 1A has a single R lobe and was chosen to illustrate our findings because the separation between the A lobe and the R lobe of the photoreceptor is clearly delineated by a prominent indentation (Stern et al., 1983). The R lobe is located to the right of the indentation. The region of this cell having the highest sensitivity to light is indicated in Fig. 1B and corresponds to the location of the R lobe (Stern et al., 1983). Figs. 1C and D show that each of the two regions that are illuminated by small spots in Fig. 1A can be independently desensitized. Thus, adaptat ion within an R lobe is localized over a distance less than the 60-#m separation of the spots in the experiment of Fig. 1. Extension of the time of adaptat ion from 9 to 70 s did
منابع مشابه
Inositol 1,4,5 trisphosphate releases calcium from specialized sites within Limulus photoreceptors
We have investigated the subcellular distribution and identity of inositol trisphosphate (InsP3)-sensitive calcium stores in living Limulus ventral photoreceptor cells, where light and InsP3 are known to raise intracellular calcium. We injected ventral photoreceptor cells with the photoprotein aequorin and viewed its luminescence with an image intensifier. InsP3 only elicited detectable aequori...
متن کاملDistinct lobes of Limulus ventral photoreceptors. II. Structure and ultrastructure
The structure of Limulus ventral photoreceptors fixed in situ has been investigated using light and electron microscopy and computer-assisted reconstruction and planimetry. Photoreceptors occur singly and in clusters. All photoreceptors have two types of lobes. The rhabdomeral lobe (R lobe) appears to be specialized for light sensitivity, containing the rhabdomere, which completely covers its e...
متن کاملRapid coupling of calcium release to depolarization in Limulus polyphemus ventral photoreceptors as revealed by microphotolysis and confocal microscopy.
Microphotolysis and confocal microscopy were used to investigate the timing of calcium release and of the electrical response in Limulus polyphemus ventral photoreceptors. The fluorescent dyes Fluo-3 and Calcium Green-5N were used to monitor local Ca2+ elevations. Photolysis of caged inositol trisphosphate (InsP3) close to the plasma membrane of the light-sensitive rhabdomeral (R-) lobe resulte...
متن کاملRelationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes
The possible role of Ca ions in mediating the drop in sensitivity associated with light adaptation in Limulus ventral photoreceptors was assessed by simultaneously measuring the sensitivity to light and the intracellular free Ca concentration (Cai); the latter was measured by using Ca-selective microelectrodes. In dark-adapted photoreceptors, the mean resting Cai was 3.5 +/- 2.5 microM SD (n = ...
متن کاملLocal adaptation in the ventral photoreceptors of Limulus
Local adaptation was demonstrated in the ventral photoreceptors of Lumulus using either flashes or continuous illumination. Spots of light locally desensitized the region of the photoreceptor on which they were focused. In dark-adapted photoreceptors where "quantum bumps" were clearly discernible, local adaptation of the quantum bumps was observed. Local adaptation could induce differences of t...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- The Journal of General Physiology
دوره 81 شماره
صفحات -
تاریخ انتشار 1983