The nss mutation or lanthanum inhibits light-induced Ca2+ influx into fly photoreceptors.

Abstract

Ion-selective calcium microelectrodes were inserted into the compound eyes of the wild-type sheep blowfly Lucilia or into the retina of the no steady state (ms) mutant of Lucilia. These electrodes monitored light-induced changes in the extracellular concentration of calcium (A[Ca2+] minimum within 6 s after light onset, and then rose to a nearly steady-state phase below the dark concentration. When lights were turned off, a rapid increase in [Ca2+]o was observed, reaching a peak above the dark level and then declining again to the dark level within 1 rain. In analogy to similar studies conduced in the honeybee drone, we suggest that the reduction in [Ca2÷]o reflects light-induced Ca 2÷ influx into the photoreceptors, while the subsequent increase in [Ca~÷]o reflects the activation of the Na-Ca exchange which extrudes Ca ~+ from the cells. In the ms mutant in response to intense prolonged light, the receptor potential declines to baseline during light while the Ca 2+ signal is almost abolished, revealing only a short transient reduction in [Ca~+]o. Application of lanthanum (LaSt), but not nickel (Ni2+), into the retinal extracellular space of normal Lucilia mimicked the effect of the ms mutation on the receptor potential, while complete elimination of the Ca ~+ signal in a reversible manner was observed. The results suggest that La 3+ and the ms mutation inhibit light-induced Ca ~+ influx into the photoreceptor in a manner similar to the action of the trp mutation in Drosophila, which has been shown to block specifically a light-activated Ca 2+ channel necessary to maintain light excitation.

Genetic dissection of light-induced Ca2+ influx into Drosophila photoreceptors.

“…The basic method applied to the large flies has been described in detail previously Kirschfeld, 1988, 1991;Rom-Glas et al, 1992). The Drosophila preparation was identical to that for intracellular recordings.…”

“…A complementary, independent method for measuring Ca 2+ mobilization in the intact eye is the use of Ca2+-selective microelectrodes for measuring changes in external Ca z+. It has been shown in several studies that, due to the small volume of retinal extracellular space in insects, large changes in Ca 2+ concentration ([ACa2+]o) can be measured during and after light (Orkand, Dietzel, and Coles, 1984;Minke and Tsacopoulos, 1986;Ziegler and Walz, 1989;Sandier and Kirschfeld, 1988, 1992Rom-Glas, Sandier, Kirschfeld, and Minke, 1992). The initial decrease in [Ca2+]o was interpreted as light-induced Ca 2+ influx into the photoreceptors and the subsequent return of [Ca2+]o towards baseline during or after light was interpreted as due to activation of Na+-Ca 2+ exchanger, extruding Ca z+ from the cell (Minke and Tsacopoulos, 1986;Ziegler and Walz, 1989).…”

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

“…Therefore, in an intact eye, Ca i will not only depend on processes inside the photoreceptors themselves, but also on the ionic conditions in the extracellular space. With respect to Ca 2+ , these can vary considerably (Sandler and Kirschfeld, 1988, 1991; Ziegler and Walz, 1989; Rom-Glas et al, 1992; Peretz et al, 1994 a ).…”

“…Both of these techniques are likely to strongly influence the extracellular ion concentrations and hence to affect Ca i . In an alternative approach, the light dependence of the Ca 2+ homeostasis in insect photoreceptors has been studied via measurements of the Ca 2+ concentration in the extracellular space (Sandler and Kirschfeld, 1988, 1991, 1992; Rom-Glas et al, 1992; Peretz et al, 1994 a ); however, the possibly strong influence of intracellular Ca 2+ buffering (Hardie, 1996 a ) and of Ca 2+ release from intracellular stores (Walz et al, 1995; Hardie, 1996 b ) on Ca i could not be studied in this way.…”

Induction of contracture and extracellular Ca2+ influx in cardiac muscle by sanguinarine: a study on cardiotoxicity of sanguinarine

“…However, it was also noted by several researchers that these ions might have different sensitivities toward different types of channels in different cells. For example, La 3+ but not Ni 2+ inhibit light-induced Ca 2+ influx into fly photoreceptors [35], and La 3+ is more potent than Ni 2+ in P2Y2-receptor-mediated activation of Ca 2+ entry pathway in the human airway epithelium [36]. Whether the SANGinduced Ca 2+ influx is specifically inhibited by La 3+ or expressing differential sensitivity toward these ions is unclear at this moment.…”