Protein kinase C‐induced disorganization and endocytosis of photosensitive membrane in Limulus ventral photoreceptors

Abstract

Protein kinase C (PKC) desensitizes the light response in photoreceptors from the ventral optic nerve of the horseshoe crab Limulus. Photoisomerization of Limulus rhodopsin leads to phosphoinositide hydrolysis, resulting in the production of inositol trisphosphate and diacylglycerol (DAG). Inositol trisphosphate mobilizes intracellular stores of Ca(2+), resulting in photoreceptor excitation in Limulus, while DAG may activate PKC. We investigated whether PKC-mediated desensitization of the photoresponse is accompanied by ultrastructural changes in the rhodopsin-bearing photosensitive membrane (rhabdom) in Limulus ventral photoreceptors. PKC activation by (-)-indolactam V in darkness induces disorganization and swelling of the rhodopsin-containing microvilli and endocytosis of rhabdomeral membrane. The effects of (-)-indolactam V on dark-adapted photoreceptor ultrastructure are reversible, are stereospecific, are blocked by coapplication of PKC inhibitors, and closely match those induced by continuous, bright light. Rhabdom disorganization and endocytosis via PKC activation may, therefore, contribute to desensitization of the light-adapted photoreceptor.

Desensitization of the photoresponse in Limulus ventral photoreceptors by protein kinase C precedes rhabdomere disorganization and endocytosis

“…is directly proportional to membrane surface area, we determined the effect of (Ϫ)-ILV on C m . Strong illumination of photoreceptors induces similar ultrastructural disorganization of microvilli to that seen following treatment with 25 mM (Ϫ)-ILV (Herman, 1991b;Dabdoub et al, 2002). The electrical response to a very dim flash (Ϫ5 log 10 units, 20-ms duration; delivering approximately 100 effective photons) was recorded and C m was estimated from the initial rate of voltage change during a Ϫ5 nA current step from the same cell (Brown & Coles, 1979).…”

“…PKC, which is activated by DAG resulting from receptor-mediated hydrolysis of inositol phospholipids, phosphorylates a variety of target proteins. We have previously established that activation of endogenous PKC desensitizes the phototransduction cascade in Limulus ventral nerve photoreceptors and leads to the disorganization and endocytosis of photosensitive membrane (Dabdoub & Payne, 1999;Dabdoub et al, 2002). Furthermore, pharmacological PKC activation can substitute for light to induce photosensitive membrane (rhabdom) turnover in several invertebrate species (Minke et al, 1990;Blest et al, 1992Blest et al, , 1993Jinks et al, 1996).…”

“…Dabdoub et al We have also previously shown that prolonged activation of PKC by (Ϫ)-ILV causes reversible photosensitive membrane disorganization and endocytosis (Dabdoub et al, 2002). Dabdoub et al We have also previously shown that prolonged activation of PKC by (Ϫ)-ILV causes reversible photosensitive membrane disorganization and endocytosis (Dabdoub et al, 2002).…”

Vitellogenesis in the Fruit Fly,Drosophila melanogaster:Antagonists Demonstrate that the PLC, IP3/DAG, PK-C Pathway is Triggered by Calmodulin

“…PK-C is known to function in endocytosis ( Dabdoub et al 2002 ; Gusarova et al 2009 ). Treatment with staurosporine has been shown to inhibit PK-C activity and block endocytosis ( Abreu et al 2008 ), and it proved capable of stopping endocytic uptake in the present experiments.…”

“…Treatment with staurosporine has been shown to inhibit PK-C activity and block endocytosis ( Abreu et al 2008 ), and it proved capable of stopping endocytic uptake in the present experiments. Both [Ca 2+ ] i increase and DAG are known to stimulate activity of PK-C ( Dabdoub et al 2002 ). Involvement of PK-C may also be inferred from the action of verapamil or CdCl 2 (CdCl 2 data not shown), each of which have frequently been used to prevent increase in cytosolic Ca 2+ , and each of which were found to terminate Vg uptake.…”