calciumchannels
Table of Contents
Calcium channels
see also calcium channel blockers, calcium
Ca Channels:
Slow voltage-gated:
- eg. via high [K]e or depolarising electrical stimuli;
- consists of alpha1, alpha2, beta, gamma, delta subunits;
- certain snail toxins from genus Conus & Cd/Mn cations block a wide range of Ca channel subtypes;
3 types:
- L:
- N: neural - important role in the spinal transmission of pain - blocked by omega conotoxin & ziconotide
- T: transient
Receptor-operated:
- eg. via hormones;
Stretch-operated:
- some blood vessels show increased Ca influx when stretched;
Physiology of calcium channel activation:
Vascular Smooth Muscle:
- contraction regulated by cytosolic Ca levels due to:
- voltage-gated Ca channel via depolarisation;
- receptor mediated hydrolysis of memb. phosphatidylinositol → IP3
- → incr. release of Ca from sarcoplasmic reticulum;
- → incr. Ca influx from extracellular as well;
- receptor operated Ca channels;
- incr. cytosolic Ca → incr. Ca binding to calmodulin
- → activ. of myosin light-chain kinase → Pn of myosin light chain
- → incr. interaction b/n actin & myosin → contraction;
- THUS, Ca blockers relax arterial sm.m. but have little effect on most venous beds & hence do not affect cardiac preload;
Cardiac Muscle:
- memb.depolarisation → fast Na & slow Ca channel activated
- → cytosolic Ca incr. binds to troponin → decr. inhib. effect of troponin
- → incr. interaction of actin/myosin;
- THUS, Ca blockers
- → -ve inotropy;
- → decreased automatacity & slowed conduction depend on effect on Ca channel recovery;
calciumchannels.txt · Last modified: 2008/09/14 23:56 by 127.0.0.1