Decreases in intracellular muscle pH during exercise have been associated with increased K+
release and K+
accumulation in the interstitium (Bangsbo, Madsen, Kiens, & Richter, 1996; Nordsborg, Mohr, Pedersen, Nielsen, Langberg, & Bangsbo, 2003). Spruce, Standen and Stanfield (1985) have shown that the ATP-sensitive K+
channels are less inhibited by ATP levels as intracellular H+
concentrations are increased. In isolated muscles, Matar, Nosek, Wong, and Renaud (2000) demonstrated that an acidic activation of the pH-dependent ATP-sensitive K+
channels results in increased K+
efflux. The relationship between open K+
channels and decreasing pH has been suggested as a possible cause of the contraction-induced K+
loss. Mohr, Nordsborg, Nielsen, Pedersen, Fischer, Krustrup et al. (2006) investigated the interactions between pH and interstitial K+ in vivo
. The researchers reported a significant relationship between decreasing values of intramuscular pH and increasing concentrations of interstitial K+
during intense exercise.
The accumulation of K+
in the interstitium has been demonstrated to reduce muscle excitability (Clausen, 2003). Increased extracellular K+
concentrations have also been shown to result in the inactivation of voltage-dependent Na+
channels (Clausen, 2003; Ruff, 1996). Thus, excitation failure due to interstitial K+
accumulation may be an influencing factor in the development of muscular fatigue (Fitts, 1994; Kjellmer, 1965).
The correlation between increased interstitial H+
accumulation was suggested by Street et al. (2005) as a possible explanation of the association between decreased performance and acidosis. Street et al. used induced metabolic alkalosis to investigate the relationship between interstitial H+
concentrations and K+
accumulation during high-intensity exercise to exhaustion. Significant correlations between decreased concentrations of interstitial H+
accumulation were found. Additionally, Street et al. (2005) reported significant decreases in interstitial H+
concentrations during alkalosis compared with placebo. Raymer, Marsh, Kowalchuk, and Thompson (2004) and Sostaric et al. (2006) found similar correlations, and suggested that NaHCO3
ingestion may improve cellular excitability during exercise.