K+ and Lac- distribution in humans during and after high-intensity exercise: role in muscle fatigue attenuation?

Abstract

This review describes processes for the distribution of K+ ([K+]) and lactate concentrations ([Lac-]) that are released from contracting muscle at high rates during high-intensity exercise. This results in increased interstitial and venous [K+] and [Lac-] in contracting muscle. Large and rapid increases in plasma [K+] and [Lac-] result in the transport of these ions into red blood cells (RBCs). These ions are distributed to noncontracting tissues within both the plasma and RBC compartments of blood. The extraction of K+ and Lac- from the circulation by noncontracting tissue serves to markedly attenuate exercise-induced increases in plasma [K+] and [Lac-]. This apparent regulation of the plasma compartment by noncontracting tissues helps to maintain favorable concentration gradients for the net movement of [K+] and [Lac-] into the venous side of the microcirculation from interstitial fluids of contracting muscle. This provides conditions that 1) reduce the increase in interstitial [K+], thereby decreasing the magnitude and rate of sarcolemmal depolarization, and 2) favor the sarcolemmal transport of Lac- from within contracting muscle cells, thereby regulating intracellular osmolality and H+ concentration. On cessation of exercise, net K+ uptake by recovering muscle is rapid, with 90-95% recovery of intracellular [K+] within 3.5 min, indicating a very high rate of Na+-K+ pump activity. The K+ extracted by noncontracting tissues during exercise may be slowly released during recovery. During the initial minutes of recovery, recovering muscle continues to release Lac- into the circulation, and noncontracting tissues continue to extract Lac- for up to 30 min. The uptake of Lac- by noncontracting tissues results in elevated intracellular [Lac-]. There is no evidence that Lac- extracted by noncontracting tissues is subsequently released; it is probably metabolized within these cells. We conclude that the uptake of K+ and Lac- by RBCs and noncontracting tissues regulates ion homeostasis within plasma and the interstitial and intracellular compartments of contracting muscle. The regulatory processes help to maintain the function of active muscles by delaying the onset of fatigue during exercise and to restore homeostasis during recovery.

Salbutamol effects on systemic potassium dynamics during and following intense continuous and intermittent exercise

“…However, salbutamol effects on [K + ] during intense exercise remain unclear, due to previous methodological limitations. Firstly, interpretation is difficult from studies measuring only antecubital venous [K + ] (Hostrup et al 2014a;Collomp et al 2000;Grove et al 1995;Newnham et al 1993;Van Baak et al 2000), as this can underestimate arterial [K + ] by as much as 2 mM during intense exercise, due to substantial K + clearance by forearm muscles (Lindinger 1995;McKenna et al 1997;Lindinger et al 1995;Kowalchuk et al 1988). Secondly, numerous studies measured [K + ] in blood drawn only after completion of exercise (Hostrup et al 2014a;Kalsen et al 2014;Larsson et al 1997;Grove et al 1995;Hostrup et al 2014b), when plasma [K + ] is falling precipitously (McKenna et al 1997;Sejersted and Sjøgaard 2000).…”

Potassium and lactate uptake by noncontracting tissue during strenuous exercise

“…One of the most dramatic changes in ionic balance observed during high intensity exercise is the marked increase in plasma potassium concentration ([K + ]). Exercise-induced hyperkalaemia, approaching 8 mmol/l in plasma of human athletes (Sejersted et al 1984), develops because K + efflux with repeated sarcolemmal depolarisation occurs at a rate greater than K + reuptake by Na + /K + /ATPase pumps (Sjogaard 1991;Lindinger et al 1995). In exercising horses, even greater increases in plasma [K + ], to values approaching 10 mmol/l, have been measured during strenuous treadmill exercise Snow 1988, 1992).…”

“…Another substantial change in plasma ion composition accompanying strenuous exercise is the exponential increase in plasma lactate concentration [lac -], again due to efflux from active skeletal muscle (Lindinger et al 1995). Similar to K + , efflux of lac -is a consequence of increased metabolic rate.…”

“…Similar to K + , efflux of lac -is a consequence of increased metabolic rate. However, unlike K + , intracellular [lac -] exceeds extracellular [lac -] in active muscle throughout the duration of high intensity exercise Fitts 1994;Lindinger et al 1995). The magnitude of the increase in plasma [lac -] in strenuously exercising horses, to values exceeding 40 mmol/l, also appears to be greater than in their human counterparts in which values rarely exceed 25 mmol/l (Harris and Snow 1992;Lindinger et al 1992).…”

“…However, measured increases in these subjects were limited to 6.3 and 25 mmol/l, respectively, indicating that a large amount of these ions were taken up by other tissues during strenuous exercise . Regulatory responses include uptake of K + and lac -by erythrocytes within the vascular space as well as distribution to tissues that are less active during exercise, predominantly noncontracting muscle (Lindinger et al 1990(Lindinger et al , 1995(Lindinger et al , 1999Sjogaard 1991;McKelvie et al 1991McKelvie et al , 1992 …”