Receptor potential and light-induced mitochondrial activation in blowfly photoreceptor mutants

Abstract

Summary. 1. Simultaneous measurements of the receptor potential and the light-induced mitochondrial activation were performed in white-eyed blowflies Calliphora vicina, mutant chalky, and Lucilia cuprina, mutants w r and w'nss. The intensity dependence and the temporal dynamics were investigated.2. The characteristic curve of the light-induced mitochondrial activation vs. log intensity has an S-like shape, which is much steeper than the characteristic curve of the receptor potential (the V/log I curve). The threshold intensity of mitochondrial activation elicits about a half-maximal receptor potential, while mitochondrial activation and photoreceptor potential saturate at about the same intensity.3. The time course of the mitochondrial activation induced by a light flash, i.e. the pulse-response curve, is biphasic in both mutants with normal phototransduction properties, Calliphora chalky and Lucilia wF ; the shape is slightly species dependent.4. In the phototransduction mutant Lucilia w'nss the step-responses of both the (bright) light-induced mitochondrial activation and receptor potential are quite different from the corresponding signals in Lucilia w F. The striking resemblance of the step-response of the mitochondrial activation to its pulse-response indicates that mitochondrial activation and receptor potential are intimately linked.

Light Dependence of Calcium and Membrane Potential Measured in Blowfly Photoreceptors In Vivo

“…Nevertheless, occasionally a very slight, transient increase in autofluorescence could be noticed in this background (Fig. 3 f, * ), probably due to the light-induced, transient redox changes of the flavoproteins in the photoreceptor mitochondria (Stavenga and Tinbergen, 1983; Mojet et al, 1991). Sometimes, such a small increase in fluorescence also was observed when measuring from a cell filled with the high affinity dyes (i.e., in Fig.…”

“…This holds particularly for insect photoreceptor cells, where Ca i has been shown to play a key role in the regulation of the light sensitivity (Bader et al, 1976; Autrum, 1979; Muijser, 1979; Tsukahara, 1980; Walz, 1992). More specifically, Ca i has been implicated in the control of numerous cellular processes in fly photoreceptors; e.g., in the modulation of the light-activated ion channels (Hardie, 1991, 1995 a , 1995 b ; Hardie and Minke, 1994), the activation of the Na + /Ca 2+ exchanger (Hardie, 1995 a , 1995 b ), the regulation of many enzymes involved in the transduction cascade (Selinger et al, 1993; Minke and Selinger, 1996), the activation of mitochondria (Fein and Tsacopoulos, 1988; Mojet et al, 1991), and the migration of pigment granules in the photoreceptor cells (Kirschfeld and Vogt, 1980; Howard, 1984; Hofstee and Stavenga, 1996).…”

Insect retinal pigments: Spectral characteristics and physiological functions

“…Absorbance measurements demonstrate that light adaptation causes a slight absorbance decrease at 432 nm, indicating that cyt b becomes somewhat more oxidized ( Fig. 15; Mojet, 1992). The optical changes all point to an enhanced electron flow through the respiratory chain resulting in a lightinduced increase in oxygen consumption.…”

“…This recycles the ATP necessary for the sodium pump that maintains the sodium and potassium gradients aecross the cell membrane and the calcium pump in the SMC membrane. The cell membrane, furthermore, contains voltage-dependent potassium channels and sodium--calcium exchanger molecules (modified from Mojet, 1992).…”

Light-induced changes in extracellular calcium concentration in the compound eye of Calliphora, Locusta and Apis

“…Prof. K. Kirschfeld pigment migration (Kirschfeld and Vogt 1980), as well as membrane and energy metabolism (Martin and Hafner 1986;Tinbergen and Stavenga 1987;Fein and Tsacopoulos 1988;Hamdorfet al 1988; Mojet et al 1991). Ca~, intracellular Ca 2+ concentration; Cao, extracellular Ca 2 + concentration Correspondence to."…”