Nervous system calcium channels

Physically, ion channels are tiny pores that stud the surface of all cells. The ion channels are important for, among other things, the function of muscles and the nervous system. These channels allow the passage of potassium, calcium, sodium, and chloride ions. Through a balance of electrical forces and chemical bonds, ion channels are specific for one ion for instance, a potassium ion channel will reject a sodium ion trying to enter its channel. An excellent visualization of the overall process is found at the website http //www. rockefeller.edu/pubinfo/howkion.html. It will be helpful to look at this website before going any further in the discussion. 

Carmignoto G, Pasti L, Pozzan T (1998) On the role of voltage-dependent calcium channels in calcium signaling of astrocytes in situ. J Neurosci 18 4637-4645 Cartier L, Hartley O, Dubois-Dauphin M, Krause KH (2005) Chemokine receptors in the central nervous system role in brain inflammation and neurodegenerative diseases. Brain Res Brain Res Rev 48 16 2... 

Burnashev, N (1996) Calcium permeability of glutamate-gated channels in the central nervous system. Curr. Opin. Neurohiol. 6 311-317. 

Potential central nervous system indications for calcium channel antagonists... 

Biochemical site of action Site 1 on voltage-dependent sodium channel Site 5 on voltage-dependent sodium channel Catalytic subunit of phosphorylase phosphatases Kainate receptor in central nervous system Unknown Ciguatoxin site 5 on voltage-dependent sodium channel Maitotoxin calcium channels... 

F. Matsumura, sponsored by the National Institute of Environmental Health Sciences (NIEHS), plans to study the toxic effects of chlorinated and pyrethroid pesticides primarily on calcium and sodium regulating processes in the nervous system. To examine the interactions of the pesticides with calcium regulating processes, researchers will use synaptosomal preparations from the brains of rats and the central nervous systems of squid. To examine the interactions of the pesticides with sodium regulating processes, they will collect antibodies directed against sodium channel proteins. 

Bullock R, Zauner A, Woodward J, Young HP (1995) Massive persistent release of excitatory amino acids following human occlusive stroke. Stroke 26 2187-2189 Burnashev N (1996) Calcium permeability of glutamate-gated channels in the central nervous system. Curr Opin Neurobiol 6 311-317... 

The directly acting vasodilators, with the exception of calcium channel antagonists and sympathetic nervous system depressants, receive the bulk of attention in this chapter. Other chapters offer additional information on diuretics (see Chapter 21), the renin-angiotensin system (see Chapter 18), adrenergic receptor antagonists (see Chapter 11), and the calcium channel antagonists (Chapter 19). 

The cardiovascular effects of local anesthetics result in part from direct effects of these drugs on the cardiac and smooth muscle membranes and from indirect effects on the autonomic nervous system. As described in Chapter 14, local anesthetics block cardiac sodium channels and thus depress abnormal cardiac pacemaker activity, excitability, and conduction. At extremely high concentrations, local anesthetics can also block calcium channels. With the notable exception of cocaine, local anesthetics also depress myocardial contractility and produce direct arteriolar dilation, leading to systemic hypotension. Cardiovascular collapse is rare, but has been reported after large doses of bupivacaine and ropivacaine have been inadvertently administered into the intravascular space. 

The acute toxic properties of all the organochlorine pesticides in humans are qualitatively similar. These agents interfere with inactivation of the sodium channel in excitable membranes and cause rapid repetitive firing in most neurons. Calcium ion transport is inhibited. These events affect repolarization and enhance the excitability of neurons. The major effect is central nervous system stimulation. With DDT, tremor may be the first manifestation, possibly continuing to convulsions, whereas with the other compounds convulsions often appear as the first sign of intoxication. There is no specific treatment for the acute intoxicated state, and management is symptomatic. 

Antihypertensive Agents. Hypertension (high blood pressure) is a significant risk factor for cardiovascular diseases such as angina heart attacks, and strokes. /(-Adrenoceptor (adrenergic nervous system receptors of the /(-type) antagonists (/(-blockers), calcium channel blockers, angiotensinconverting enzyme (ACE) inhibitors, and potassium channel activators... 

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