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calciumchannels

Calcium channels

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: 2008/09/15 09:56 (external edit)