there are 800 genes in this family in the mammalian genome g-protein coupled receptors
TRANSCRIPT
There are 800 genes in this family in the mammalian genome
G-Protein Coupled Receptors
Orphan Receptors in the GPCR family
Rhodopsin and b-adrenergic receptor found to be homologous
“Artisanal Period”: Using known ligands to find their GPCR’s dopamine, adenosine; angiotensin, vasopressin etc
“De-orphanisation” Using GPCR to find new transmitters e.g. nociceptin, ghrellin
Industrial approach, many ligands and receptors identifiedolfactory ligands, taste receptors, H+, Ca++
Still; the majority of GPCR do not have known ligands; so they have been given numbers
De-orphanization Protocols
Many industrial approaches but most depend on the following
Express GPCR of interest in a cell line which has the requisite signalingsystem, e.g. increase in Ca
Use extracts of organs or blood to see if they activate the signalPurify the fraction that does it using this assay
Tularik Co, wanted to find the ligands for GPCR 91, and GPCR 99
They are homologous to the Purinergic (ATP) receptors
But after much search the activity in the kidney turned out to be
Succinate for GPR91 and -ketoglutarate for GPR99
Nature. 2004 ;429:188-93
Krebs Cycle
GPR91 GPR99
GPR91 GPR99
Highest expression is in the Kidney
Mostly Proximal Tubule and JGA Mostly Distal Tubule
Succ
-KG
Normal
Nx
Isolated Perfused JGA
In Isolated Perfused JGA : High Glucose increases renin release
In Isolated Perfused JGA : Perfusion of Succinate increases renin release
Fluorocitrate
Renin release in Isolated Perfused JGASuccinate in the bath is faster than high glucose
Succinate Levels in Diabetic Urine and Kidneys
Renin Release from Isolated perfused JGA preparation
GPR91 RECA-1 Merged
High Glucose and Succinate increase cell Calcium in isolated endothelial cells
High Glucose and Succinate increase cell Calcium via GPR91 in isolated glomerular endothelial cells
High Glucose or Succinate increase cell CaIn isolated glomeruli
High Succinate increase PGE2 production
+/+ -/-
Control
STZDiabetes
Diabetes increases renin granule content only in GPR91+ mice
