title: Electrophysiological measurement of the number of rhodopsin molecules in single Limulus photoreceptors.
abstract: Two partly independent electrophysiological methods are described for measuring the number of rhodopsin molecules (R) in single ventral photoreceptors. Method 1 is based on measurements of the relative intensity required to elicit a quantal response and the relative intensity required to half-saturate the early receptor potential (ERP). Method 2 is based on measurements of the absolute intensity required to elicit a quantal response. Both methods give values of R approximately equal to 10(9). From these and other measurements, estimates are derived for the surface density of rhodopsin (8,000/micrometer2), the charge movement during the ERP per isomerized rhodopsin (20 X 10(-21) C), and the half-time for thermal isomerization of rhodopsin (36yr).
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology / Q000379:methods; D006737:Horseshoe Crabs; D066298:In Vitro Techniques; D007536:Isomerism; D008027:Light; D008564:Membrane Potentials; D010786:Photoreceptor Cells / Q000032:analysis* / Q000502:physiology; D011789:Quantum Theory; D012168:Retinal Pigments / Q000032:analysis*; D012243:Rhodopsin / Q000032:analysis* / Q000502:physiology; D013816:Thermodynamics
chemical_list: D012168:Retinal Pigments; D012243:Rhodopsin