A role for hydrolysis of inositol 1,4,5-trisphosphate in terminating the response to inositol 1,4,5-trisphosphate and to a flash of light in Limulus ventral photoreceptors.
Injection of inositol 1,4,5-trisphosphate (Ins 1,4,5-P3) into Limulus ventral photoreceptors produces excitation similar to that produced by light. One process which might contribute to rapid termination of the responses to Ins 1,4,5-P3 and to light is the hydrolysis of Ins 1,4,5-P3 by an InsP3-5-phosphatase to form inositol 1,4-bisphosphate. Inositol 2,4,5-trisphosphate (Ins 2,4,5-P3) is known to be less hydrolysable by the InsP3-5-phosphatase than is Ins 1,4,5-P3. Whereas ventral photoreceptors respond to an injection of Ins 1,4,5-P3 with a single wave of depolarization, the response to Ins 2,4,5-P3 is a burst of waves of depolarization. Our hypothesis is that it is the resistance to hydrolysis by the InsP3-5-phosphatase which accounts for the burst of waves produced by Ins 2,4,5-P3. To test this idea we injected ventral photoreceptors with Ins 1,4,5-P3 in the presence of the non-specific phosphatase inhibitors, vanadate and fluoride, which prolong the response to a flash of light in ventral photoreceptors (D.W. Corson, A. Fein, W.W. Walthall, J. Gen. Physiol. 82 (1983) 659-677). In the presence of fluoride or vanadate the response to Ins 1,4,5-P3 was composed of a burst of waves rather than a single wave of depolarization. We conclude that hydrolysis of Ins 1,4,5-P3 by the InsP3-5-phosphatase plays a role in terminating the ventral photoreceptors response to Ins 1,4,5-P3 and also to light.
Vallet
A M
AM
Department of Physiology, University of Connecticut Health Center, Farmington 06030-3505, USA.
Fein
A
A
D000222:Adaptation, Physiological / Q000187:drug effects / Q000528:radiation effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006737:Horseshoe Crabs; D006868:Hydrolysis; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D017956:Photoreceptor Cells, Invertebrate / Q000187:drug effects* / Q000528:radiation effects; D014638:Vanadates / Q000494:pharmacology
D014638:Vanadates; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium