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This is about smooth muscles.

I know that the Voltage-operated Ca²+ channels on the smooth muscle membrane can be opened by membrane depolarization to threshold. I also know that this depolarization in question can be brought about by opening of receptor-operated calcium channels on the plasma membrane.(1) What I am curious to know, however, is whether the Ca²+ released into the cytoplasm (sarcoplasm) when say IP3 binds to its receptor on the Sarcoplasmic reticulum can (on its own, without any other thing happening) cause depolarization of the membrane potential to threshold and subsequently lead to opening of the Voltage-operated Ca²+ channels on the muscle cell plasma membrane. I am asking this because most often, the IP3-mediated Calcium release is discussed almost entirely as an accessory pathway for Calcium release, being only able to supplement an existing Calcium current.

(1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2652144/#!po=4.24837

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    $\begingroup$ The membrane potential is not determined by ionic concentrations but by ionic permeability, so I would assume that it doesn't change. $\endgroup$
    – BPinto
    Commented Mar 24, 2021 at 0:32
  • $\begingroup$ Oh! Yes. You're right $\endgroup$
    – Chemo-Mike
    Commented Mar 26, 2021 at 15:35

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