title: The phosphoinositide signaling cascade is involved in photoreception in the leech Hirudo medicinalis.
abstract: The effects of BAPTA, heparin, and neomycin on electrical light responses were studied in the photoreceptors of Hirudo medicinalis. Light activation produces a fast increase in intracellular Ca2+ concentration (Cai) as detected with the fluorescent Ca2+ indicator calcium green-5N. Chelating intracellular calcium by injections of 10 mmol(-1) BAPTA suppresses spontaneous quantum bumps, reduces light sensitivity by more than 2 log(10) units, and substantially increases the latent period of light responses. BAPTA strongly inhibits the plateau phase of responses to long steps of light. Injections of 45-100 mg ml(-1) of heparin act in a similar manner to BAPTA, affecting the latency of the light responses even more. De-N-sulfated heparin, an inactive analog, is almost ineffective at the same concentration compared with heparin. Heparin diminishes the light-induced Cai elevation significantly, whereas de-N-sulfated heparin does not. Intracellular injections of 50-100 mmol l(-1) of the aminoglycoside neomycin, which inhibits phospholipase-C-mediated inositol 1,4,5-trisphosphate formation, acts similar to BAPTA and heparin. Pressure injections of the hydrolysis resistant analog of inositol 1,4,5-trisphosphate, inositol 2,4,5-trisphosphate, strongly depolarize leech photoreceptors and mimic an effect of light adaptation. These results suggest a close similarity between phototransduction mechanisms in leech photoreceptors and existing models for visual transduction in other invertebrate microvillar photoreceptors.
authors: Institut für Biochemie und Biologie, Tierphysiologie, Universität Potsdam, Germany.
authors: K
authors: K
authors: Ukhanov
authors: B
authors: B
authors: Walz
mesh_terms: D000818:Animals; D000925:Anticoagulants / Q000008:administration & dosage / Q000494:pharmacology; D002614:Chelating Agents / Q000008:administration & dosage / Q000494:pharmacology; D004533:Egtazic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D006493:Heparin / Q000008:administration & dosage / Q000494:pharmacology; D007865:Leeches / Q000502:physiology*; D009355:Neomycin / Q000008:administration & dosage / Q000494:pharmacology; D010786:Photoreceptor Cells / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D015398:Signal Transduction
chemical_list: D000925:Anticoagulants; D002614:Chelating Agents; D011500:Protein Synthesis Inhibitors; D004533:Egtazic Acid; D006493:Heparin; D009355:Neomycin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid