AGONISTS AND ANTAGONISTS Flashcards
DRUGS CAN MAINLY BE CLASSIFIED AS …………………… OR ……………………………
AGONIST
ANTAGONIST
OCCUPANCY OF A RECEPTOR BY A DRUG MOLECULE MAY OR MAY NOT RESULT IN ………………………… OF THE RECEPTOR
ACTIVATION
WHAT IS OCCUPANCY GOVERNED BY
AFFINITY
WHAT IS ACTIVATION GOVERERNED BY
EFFICACY
WHAT IS AFFINITY
HOW WELL A DRUG BINDS TO A RECEPTRO
WHAT IS EFFICACY
HOW WELL A DRUG ACTIVATES A RECEPTOR TO EVOKE A RESPONSE
DEFINE OCCUPANCY
PROPORTION OF RECEPTORS OCCUPIED WILL VARY WITH DRUG CONC.
IE
NO. OF RECEPTORS OCCUPIED/TOTAL NO. OF RECEPTORS AVAILABLE
IN THEORY A HIGH OCCUPANCY SHOULD PRODUCE A LARGER RESPONSE. WHY IS THIS NOT ACCURATE
- THIS DOES NOT WORK FOR ANTAGONISTS AS THEY DO NOT EVOKE A RESPONSE
- AGONIST OCCUPANCY AND RESPONSE ARE NOT DIRECT BECAUSE EFFICACY IS THE DETERMINING FACTOR NOT AFFINITY
HOW CAN WE MEASURE OCCUPANCY AND DEDUCE AFFINITY
RADIOLIGAND BINDING ASSAY
WHAT IS A RADIOLIGAND BINDING ASSAY
- SAMPLE THAT CONTAINS A POI
- CREATE A RADIOACTIVE VERSION OF THE DRUG WE WANT TO TEST ON THE POI
- INCUBATE THE MIXTURE TO REACH EQUILIBRIUM
- FILTER AND WASH AWAY NON BOUND (EXCESS) LIGAND
- MEASURE THE RADIOACTIVITY LEFT BEHIND (SO WE CAN MEASURE THE RADIOACTIVE DRUG BOUND TO THE RECEPTORS
- THIS IS DONE WITH TWO SETS OF TEST TUBES
- WILL HAVE SPECIFIC BINDING AND NON
SPECIFIC BOUND RADIOACTIVE DRUG - WILL HAVE ONLY NON SPECIFIC RADIOACTIVE
BOUND DRUG
CAL 1- 2 = SPECIFIC BINDING
- WILL HAVE SPECIFIC BINDING AND NON
HOW MUCH NON SPECIFIC BINDING SHOULD A GOOD DRUG HAVE
AS LITTLE AS POSSIBLE
WHAT MAKES FOR A GOOD RADIOLIGAND BINDING EXPERIMENT
THE MODIFIED VERSION OF THE DRUG MUST BEHAVE EXACTLY AS BEFORE
THE DRUG MUST BE EXTREMELY PURE
WE MUST PREVENT DEGRADATION OF THE DRUG
WE MUST CONSIDER THE RADIOACTIVE LABEL WE ARE USING
HOW DO YOU PREVENT DEGRADATION OF A DRUG
FREE RADICAL SCAVENGER IN DRUG SOLUTION
AVOIDING LIGHT
STORE AT A LOW TEMPERATURE
INCORPORATION OF AN ANTIOXIDANT
WHAT ARE THE ADVANTAGES OF USING TRITIUM IN A RADIOLIGAND BINDING ASSAY
DOES NOT CHANGE CHEMICAL NATURE
LONG HALF LIFE
STABLE
WHAT ARE THE DISADVANTAGES OF USING TRITIUM IN A RADIOLIGAND BINDING ASSAY
DANGEROUS TO WORK WITH SO SPECIAL LABS NEEDED
DIFFICULT AND EXPENSIVE TO LABEL
WHAT ARE THE ADVANTAGES OF USING I125 IN A RADIOLIGAND BINDING ASSAY
SAFER
IODINATION EASY AND CHEAP
WHAT ARE THE DISADVANTAGES OF USING I125 IN A RADIOLIGAND BINDING ASSAY
DEGRADES MORE QUICKLY
INTERFERES WITH LIGAND MORE
SHORTER HALF LIFE
WHAT ARE SOME OF THE PROBLEMS FACED WHEN TRYING TO PRESERVE A POI THAT HAS BEEN PURIFIED IN CENTRIFUGE
A CELL MIGHT RELEASE CONTENTS SUCH AS ENZYMES THAT MAY BREAK DOWN THE POI
HOW CAN WE PRESERVE THE POI IN A RADIOLIGAND BINDING ASSAY
ADDING PROTEASE INHIBITORS
KEEPING THE CELL WHOLE
LOW TEMPERATURES
LIGAND BINDING ASSAY DEPEND ON THE MIXTURE REACHING …………………….
EQUILIBRIUM
IF A LIGAND HAS A LOW AFFINITY THEN WHAT CAN BE SAID ABOUT EQUILIBRIUM
IT HAS A FAST BACK RATE AKA SEPARATES FROM THE LIGAND QUICKLY
IF A LIGAND IN A BINDING ASSAY HAS A FAST BACK RATE WHAT IMPACT DOES IT HAVE ON THE EXPERIMENT
IT IS DIFFICULT TO MEASURE
WHAT IS SHOWN IN RADIOLIGAND BINDING CURVES
RADIOACTIVITY AGAINST CONCENTRATIONS
PLOTS: TOTAL BOUND, NON SPECIFIC BINDING, SPECIFIC BINDING
WHAT IS THE KD
A CONSTANT FOR MEASURE OF AFFINITY
HOW CAN YOU FIND THE KD
FROM THE SCATCHARD EQUATION OR ON A RADIOLIGAND BINDING CURVE AT 50%
WHAT IS THE SCATCHARD EQUATION
BOUND/FREE = (BMAX-BOUND)/KD
WHERE BMAX IS TOTAL BINDING
WHAT IS SHOWN IN A SCATCHARD PLOT
BOUND RADIOLIGAND AGAINST B/F
THE X INTERCEPT = BMAX
THE SLOPE = -1/KD
