Stephanie A. Sontag1, Justin X. Nicoll2, Eric M. Mosier3, Andrew C. Fry1

1University of Kansas, Lawrence, KS; 2 California State University, Northridge, CA; 3 Northwest Missouri State University, Maryville, MO.

Studies suggest that the NaK pump plays an important role in muscle fatigue. While changes in the quantity and characteristics of the NaK pumps have been shown to enhance or inhibit muscle contractility, few data are available on NaK pump subunits α1, α2, or β1 expression in humans in response to exercise. A knockout model of the α2 subunit in mice suggests that muscle use regulates the α2 subunit giving skeletal muscle the ability to maintain force while resisting fatigue. PURPOSE: The purpose of this study was to examine the acute responses in the expression of NaK pump α1, α2, and β1 subunits in trained men after a resistance exercise (RE) bout. METHODS: Resistance trained men (n=16; , age=21 yrs, height=167.5 cm, body mass=80.85 kg, squat 1 repetition maximum (1RM)=138.9 kg, training history=5.1 yrs) participated in a RE bout. Before the RE visit, subjects came in for a 1RM strength test for barbell back squat according to NSCA guidelines (Baechle and Earle 2008). Subjects performed an RE bout consisting of 5 sets of barbell speed squats for 5 repetitions at 60% of their 1RM with two minutes of rest in between sets, followed by 3 sets of 10 repetitions of leg extensions at 70% 1RM. Biopsies from the VL were collected before (PRE) the RE bout and 10 min after cessation of exercise (POST). Subunit content was found using western blotting and an infrared imaging system. RESULTS: Results are presented in Figure 1. There was a significant decrease in the α2 subunit expression after an RE bout. There was no significant change in the α1 subunit expression. Although not statistically significant, there was a moderate effect size for the increase in β1 subunit expression (Cohen’s D=0.66). CONCLUSION: The α2 subunit expression decreases as an acute response to this RE protocol. The α1 subunit expression appears to remain constant, and it is still unclear if there is an acute response of the β1 subunit expression to RE.

Sontag Figure 1.docx (89 kB)
Sontag Figure 1

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