Calcium action sites

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... 

Schematic diagram of a cardiac muscle sarcomere, with sites of action of several drugs that alter contractility (numbered structures). Site 1 is Na+/K+ ATPase, the sodium pump. Site 2 is the sodium/calcium exchanger. Site 3 is the voltage-gated calcium channel. Site 4 is a calcium transporter that pumps calcium into the sarcoplasmic reticulum (SR). Site 5 is a calcium channel in the membrane of the SR that is triggered to release stored calcium by activator calcium. Site 6 is the actin-troponin-tropomyosin complex at which activator calcium brings about the contractile interaction of actin and myosin.

P/Q-type channels undergo a second calcium-dependent process whereby current activity increases following a strong membrane depolarization or a train of action potentials. This increase is only observed in the presence of external calcium, is insensitive to calcium buffers, and requires the high-affinity calcium binding sites on calmodulin (Chaudhuri et al. 2004 DeMaria et al. 2001). This process, termed calcium-dependent facilitation (CDF), is not observed with N-type or R-type channels and is Cav2.1 channel splice isoform dependent (Chaudhuri et al. 2004). The... 

Factors controlling calcium homeostasis are calcitonin, parathyroid hormone(PTH), and a vitamin D metabolite. Calcitonin, a polypeptide of 32 amino acid residues, mol wt - SGOO, is synthesized by the thyroid gland. Release is stimulated by small increases in blood Ca " concentration. The sites of action of calcitonin are the bones and kidneys. Calcitonin increases bone calcification, thereby inhibiting resorption. In the kidney, it inhibits Ca " reabsorption and increases Ca " excretion in urine. Calcitonin operates via a cyclic adenosine monophosphate (cAMP) mechanism. 

Other systems also interact with glutamate. Activation of L-type voltagegated calcium channels (VGCC) occurs with NMDA receptor activation. Lamotrigine blocks several ion channels, including P- and N-type VGCC channels, an action that blocks the euphoric effects of ketamine and reduces dysphoric and cognitive effects (Hundt et al. 1998). Other modulatory sites,... 

Oral bisphosphonates are poorly absorbed (less than 5%). Taking them in the presence of food or calcium supplementation further reduces absorption. After absorption, bisphosphonate uptake to the primary site of action is rapid and sustained. Once attached to bone tissue, bisphosphonates are released very slowly. These drugs are not metabolized and are excreted renally. They are not recommended for use in patients with renal insufficiency. 

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