Which statement about cardiac muscle cells is true? A) The DHP proteins are in the sarcoplasmic reticulum membrane. B) There is a physical connection between DHP and ryanodine receptors. C) The T tubules are smaller than those of skeletal muscle cells. D) Ryanodine receptors are ion-gated Na⁺ channels. E) Extracellular Ca²⁺ flows into the cytoplasm through DHP channels and then opens calcium channels in the sarcoplasmic reticulum.

Question

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Extracellular Ca²⁺ enters cardiac muscle cells through DHP channels (L-type calcium channels) and triggers the opening of ryanodine receptors on the sarcoplasmic reticulum, releasing more Ca²⁺ into the cytoplasm.

Which Statement About Cardiac Muscle Cells Is True