Human skeletal muscle plasmalemma alters its structure to change its Ca²⁺-handling following heavy-load resistance exercise.

Abstract

High-force eccentric exercise results in sustained increases in cytoplasmic Ca²⁺ levels ([Ca²⁺]_cyto), which can cause damage to the muscle. Here we report that a heavy-load strength training bout greatly alters the structure of the membrane network inside the fibres, the tubular (t-) system, causing the loss of its predominantly transverse organization and an increase in vacuolation of its longitudinal tubules across adjacent sarcomeres. The transverse tubules and vacuoles displayed distinct Ca²⁺-handling properties. Both t-system components could take up Ca²⁺ from the cytoplasm but only transverse tubules supported store-operated Ca²⁺ entry. The retention of significant amounts of Ca²⁺ within vacuoles provides an effective mechanism to reduce the total content of Ca²⁺ within the fibre cytoplasm. We propose this ability can reduce or limit resistance exercise-induced, Ca²⁺-dependent damage to the fibre by the reduction of [Ca²⁺]_cyto to help maintain fibre viability during the period associated with delayed onset muscle soreness.