ION CHANNELS ::
Ion channels are the components of both intracellular and extracellular membranes with variable selectivity to permeate various ions notably the physiological cations Na+ K+ Ca2+ and Mg2+ and the anion Cl- in response to cell stimuli Interest in ion channel research began increasing in mid 1970s during this decade Na - channels received the greatest attention one of the reasons was the availability of clinically useful drugs that block Na channels including the antiarrhythmics and local anaesthetics like procaine in the early to mid 1980s selective Ca- channel blockers such as diltiazem verapamil and nifedipine became available through out the word for the treatment at hypertension The interest in potasium(K+) Channels began increasing dramatically in 1984 with the identification of selective k+ channel modulators like pinacidil cromakalim and nicorandil and the establishment of the link between insulin release from b-cell and potassium channels
Each ion channel irrespective of the type consists of a pore with selective filter a gate that opens or closes to permeate ion and sensors that permit the channels to respond to cell signals in fact ion channels are no longer pores but made up of glycoproteins in cell membrane containing receptors
The relative activity of ion channels depend upon a number of factors like charge size of hydrated and unhydrated ions hydration energy and affinity for binding sites that are components of the channel
The channels may be classified depending upon the stimuli to which the channels are sensitive electrophysiological features or the nature of ions they permeate likewise we have sodium channels potassium channels calcium channels etc The opening of potassium or chloride ions produce hyperpolarization or inhibitory effect whereas sodium and calcium channels produce depolarization and are of excitatory nature
0 Comments