when Ca2+ channels are used versus Na+ channels, connection?

[luctoretemergo]

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I'm a little confused about when Ca2+ channels are used versus Na+ channels.

Are Na channels used just in resting potential/action potential, and Ca channels use in the synaptic system? I know how both work but I'm having issues connecting the two or determining which is found where.

I'm thinking that the action potential of the Na channels (depolarization, repolarization, to resting) causes the opening of the Ca2 channels in neuronal membranes, but I'm not sure.

Thanks.

 

[PiBond]

I'm a little confused about when Ca2+ channels are used versus Na+ channels.

Are Na channels used just in resting potential/action potential, and Ca channels use in the synaptic system? I know how both work but I'm having issues connecting the two or determining which is found where.

I'm thinking that the action potential of the Na channels (depolarization, repolarization, to resting) causes the opening of the Ca2 channels in neuronal membranes, but I'm not sure.

Thanks.

short answer: it really depends on the tissue type

we see voltage gated Na+ channels open in response to a stimulus in nerve cells and cardiac muscle cells, for example. in nerve cells, the VG Na+ channels allow the propagation of the action potential while in cardiac muscle cells they initiate the first step in cardiac muscle contraction (they cause the release of stores of Ca2+). while cells do contain a small amount of "regular" Na+ channels that allow Na+ to leak into the cell, the RMP isn't significantly determined by the Na+ ion...but there is a small contribution.

Ca2+ channels that are found at the synaptic terminal are voltage gated and cause the release of neurotransmitter from nerve cells. this occurs when Ca2+ flows into the cell, binds synapsin, and causes our vesicles to fuse with the presynaptic cell membrane. in addition, we also see voltage gated Ca2+ channels in autorhythmic cells in the heart. these open as a result of Na+ leak channels that depolarize the autorhythmic cells to a specific threshold. in addition, slow VG Ca2+ channels also cause the characteristic "plateau" in cardiac muscle cells.

 

[methylethyl88]

In a nerve cell, the opening and closing of fast VG Na+ channels allows for the propagation of the action potential down the axon. Once the AP reaches the presynaptic terminal of the axon, VG Ca++ channels will open up and allow Ca+ to enter the terminal. This influx of calcium will initiate the release of something (usually a hormone) from the presynaptic terminal.

Calcium channels have a variety of actions in the body and control everything from muscle contractions and fertilization of an egg to maintaining normal blood pressure and blood clotting.

 

[ilovemcat]

Simple answer - Sinoatrial Node & The Heart Cells utilize Ca+ Channels to depolarize tissue membrane.

However, Voltage-Gated Ca+ Channels near the Synaptic Cleft release Neurotransmitter Vesicles via exocytosis.

 

[fizzgig]

as an addition and also to clarify for myself:

in the case of muscle cells both Na and Ca are used. all muscle cells that contract do so by being activated by depolarization which is caused by Na inrush. that initial inrush may be caused by NT binding or in the heart gap junctions from cell to cell, or in SMM there's intercell junctions too right (i forget with SMM). the voltage change in the muscle cell THEN triggers Ca to be released from the SR within the cell which actually causes contraction til it is gathered back up. that is why the AP for muscle cells goes up quickly, peaks, and drops slightly before it levels out for a while. the initial depol is Na, like a typical AP, and Ca extends the depolarized time.