K⁺ Transport and Volume Regulatory Response by NKCC in Resting Rat Hindlimb Skeletal Muscle

Abstract

This study tested the hypothesis that the NKCC is involved in volume regulation, specifically regulatory volume increase (RVI), in resting skeletal muscle. Neurally and vascularly isolated rat hindlimbs were perfused with a bovine erythrocyte perfusate containing ⁴²K or ⁸⁶Rb as markers of unidirectional K⁺ flux across the sarcolemma. Compared to controls, perfusion with 120 µM bumetanide (a specific inhibitor of the NKCC) decreased J_inK by 15±2%, indicating the functional presence of the NKCC. Experiments with ouabain (to block active K⁺ transport by the Na,K ATPase) showed that the bumetanide-sensitive component of J_inK comprised 35% of the total ouabain-sensitive J_inK. Inhibition of NKCC resulted in a net loss of water by muscle. When hindlimbs were perfused with hypertonic (380 mOsm/L by addition of sucrose) perfusate for 20 min, after initially blocking K⁺ channels with 1 mM barium, J_inK rapidly (2-3 min) increased 2-fold followed by a rapid decline. This rapid, transient increase in J_inK was abolished with bumetanide, confirming that perfusion with hypertonic perfusate stimulated NKCC activity and RVI. The hypertonic perfusate also resulted in temporally associated decreases in net water uptake by muscle. It is concluded that a functional NKCC is present in mammalian skeletal muscle and that it is involved in cell volume regulation.

Intracellular and extracellular renin have opposite effects on the regulation of heart cell volume. Implications for myocardial ischaemia

“…14 The effect of extracellular renin plus Ao on cell volume was due to activation of the Na-K-2Cl cotransporter because bumetanide, an inhibitor of the Na-K-2Cl cotransporter, suppressed the effect of extracellular renin plus Ao on cell volume. The relationship between Na-K-ATPase and Na-K-2Cl contransporter, however, is complex and far from clear 4 and further studies are needed to clarify this relationship, particularly during heart failure.…”

“…3 The relationship between the sodium pump and the cotransporter is complex and not totally clear. 4 In skeletal muscle in culture, for instance, the Na-K-2Cl-mediated K uptake has been found to be insensitive to ouabain, at least during short incubations 5 while in skeletal muscle, in situ, ouabain abolishes the cotransporter. 5 It is known that the circulating renin angiotensin system is an important regulator of blood volume and that intracellular and extracellular renin alters cellular functions like the inward calcium current or gap junctional conductance in the failing heart 6 but no information is available if renin influences heart cell volume.…”

With-No-Lysine Kinase 3 (WNK3) stimulates glioma invasion by regulating cell volume

“…Numerous studies have demonstrated that one of the important functions of NKCC1 is regulatory volume increase (RVI), which is used to reestablish normal cell volume after cells have been shrunk by exposure to hyperosmotic conditions (9,18,32,37,42). We generated a stable knockdown of WNK3 using shRNAs (WNK3-KD) in D54 glioma cells.…”

“…WNKs have previously been implicated in volume control in tissues tasked with fluid transport such as the kidney (48,49) and epithelium (8). More recently, they have also emerged as important regulators in the brain (7,14,32) where they appear to influence the neuronal Cl Ϫ gradient, which establishes whether the activation of GABA receptors is excitatory or inhibitory. More importantly, the WNKs have been implicated in Cl Ϫ flux in various cells types and are able to phosphorylate and regulate SPAK, OSR1, and other WNK family members (1,12,28,29,48).…”

Time course and magnitude of changes in total body water, extracellular fluid volume, intracellular fluid volume and plasma volume during submaximal exercise and recovery in horses

“…The only viable explanation for a simultaneous decrease in ECFV and increase in ICFV during this period of exercise recovery is an increase in intracellular osmolality and/or decrease in extracellular osmolality. While the mechanism(s) responsible for these responses remain(s) to be determined, they may be attributed to an increase in metabolic and ionic osmolytes (glycogen, potassium) within recovering skeletal muscle, to an increase in cellular Na þ -K þ -2Cl 2 co-transporter activity in order to restore volume of non-contracting tissues 29 , and to an increase in cellular Na þ -K þ -2Cl 2 co-transporter activity in order to restore intracellular [K þ ] of recovering skeletal muscle 9,30 .…”