L-Type Calcium Channels: Small Release with Big Potential

 

L-type Ca²⁺ channels in the sarcoplasmic reticulum of skeletal muscles release small amounts of calcium, but this calcium release does not seem to be important for the contraction of a skeletal muscle. Skeletal muscle obviously needs ATP in order to properly relax and contract. This source of ATP can be made through multiple pathways, but the majority of ATP in skeletal muscles is supplied by the Tricyclic acid cycle (TCA) (Hargreaves et al., 2018). The TCA cycle, being the main supplier for ATP in skeletal muscle is greatly influenced by the presents of Ca²⁺ (Hargreaves et al., 2018). Is the small amount of calcium release from the L-type Ca²⁺channels playing a role in the activation of ATP synthesis? Metabolic pathways in the skeletal muscle cell are regulated by levels of ATP and it would make sense for the muscle itself to prime its own metabolic pathway.

The small amount of calcium release from the L-type Ca²⁺ channel is not necessary for muscle contraction, but may play an important role the longevity of muscle contraction and muscle ATP Levels. When inhibiting the L-type Ca²⁺ channel the muscle still contracts, however there is evidence that other mechanisms are affected.  Mutating the L-type Ca²⁺ channel can result in accelerated muscle fatigue and altered metabolism (Beqollari et al., 2018). The small amount of calcium release from L-type Ca2+ channels reduce muscle fatigue by activate calmodulin kinase type II (Georgiou et al., 2015). Calmodulin kinase type II influences fatty acid metabolism (Georgiou et al., 2015) that can also be a huge energy source for skeletal muscle (Hargreaves et al., 2018). The calcium levels released by the L-type Ca²⁺ channels may be small, but appears to be a big determinant in fuel choice and metabolic activation.

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