An electron microprobe analysis of photoreceptors and outer pigment cells in the retina of the honeybee drone

Summary

Intracellular concentrations of elements were measured in the retina of the honeybee drone,Apis mellifera ♂ by electron microprobe X-ray analysis of frozen dried sections (Table 2). Before shock-freezing, slices of retina were superfused with Ringer solution, as in other work in which intracellular activities of Na⁺, K⁺ and Cl⁻ were measured with ion-selective microelectrodes. The results give no evidence for any binding or sequestering of these elements in the cells, with the possible exception of K in photoreceptors (Table 3). In the special case of Na in outer pigment cells,a _Na and [Na] were measured in the same piece of tissue: Na was present at a high concentration (55 mmol/l) but, again, we calculate that it was all freely dissolved in the cell water.

It was estimated that the subrhabdomeric cisternae of the photoreceptors contained 2–3 mmol/l Ca; otherwise, their electrolyte composition was similar to that of the cytoplasm. [Na], [K] and [Cl] in the rhabdom were what would be expected if the spaces between the microvilli were filled with Ringer solution