Voltage-sensitive Ca2 channels

Presynaptic events during synaptic transmission are rapid, dynamic and interconnected. The time between Ca2+ influx and exocytosis in the nerve terminal is very short. At the frog NMJ at room temperature, 0.5-1 ms elapses between the depolarization of the nerve terminal and the beginning of the postsynaptic response. In the squid giant synapse, recordings can be made simultaneously in the presynaptic nerve terminal and in the postsynaptic cell. Voltage-sensitive Ca2+ channels open toward the end of the action potential. The time between Ca2+ influx and the postsynaptic response as measured by the postsynaptic membrane potential is 200 ps (Fig. 10-7). However, measurements made with optical methods to record presynaptic events indicate a delay of only 60 ps between Ca2+ influx and the postsynaptic response at 38°C [21]. 

FIGURE 10-7 The delay between Ca2+ influx into the nerve terminal and the postsynaptic response is brief. The temporal relationships between the Ca2+ current and the action potential in the nerve terminal and the postsynaptic response in the squid giant synapse are shown. The rapid depolarization (a) and repolarization (b) phases of the action potential are drawn. A major fraction of the synaptic delay results from the slow-opening, voltage-sensitive Ca2+ channels. There is a further delay of approximately 200 is between Ca2+ influx and the postsynaptic response. (With permission from reference [20].)... 

Although AC5 and AC6 are not influenced by Ca2+/ calmodulin, these two forms of the enzymes are inhibited by free Ca2+. The concentrations of Ca2+ required for this inhibition are in the physiological range (0.1-1.0 mmol/1) that would be observed upon activation of voltage-sensitive Ca2+ channels in neurons [ 1 ]. The localization of AC5 and AC6 in the brain indicates that this form of Ca2+ influx is the primary means of Ca2+ regulation of these enzymes. 

Miller, R.J. Voltage-sensitive Ca2+ channels. /. Biol. Chem. 267 1403-1406,1992. 

Tsang SY, Yao X, Essin K, Wong CM, Chan FL, Gollasch M, Huang Y (2004) Raloxifene relaxes rat cerebral arteries in vitro and inhibits L-type voltage-sensitive Ca2+ channels. Stroke 35(7) 1709-1714... 

Desnuelle, C., Renaud, J.F., Delpont, E., Serratrice, G., and Lazdunski, M., 1986, [3H]nitrendipine receptors as markers of a class of putative voltage-sensitive Ca2+ channels in normal human skeletal muscle and in muscle from Duchenne muscular dystrophy patients, Muscle Nerve, 9, pp 148—151. 

Ueda, K., Shinohara, S., Yagami, T., Asakura, K., and Kawasaki, K. (1997). Amyloid beta protein potentiates Ca2+ influx through L-type voltage-sensitive Ca2+ channels a possible involvement of free radicals. J Neurochem 68, 265—271. 

Bergh JJ, Shao Y, Puente E, Duncan RL, Farach-Carson MC. 2006. Osteoblast Ca2+ permeability and voltage-sensitive Ca2+ channel expression is temporally regulated by 1,25-dihydroxyvitamin D3. Am J Physiol 290 C822-31. 

Ryder KD, Duncan RL. 2001. Parathyroid hormone enhances fluid shear-induced [Ca2+]i signaling in osteoblastic cells through activation of mechanosensitive and voltage-sensitive Ca2+ channels. J Bone Miner Res 16 240-8. 

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