The influence of bumetanide on the membrane potential of mouse skeletal muscle cells in isotonic and hypertonic media

Abstract

Increasing the medium osmolality, with a non‐ionic osmoticant, from control (289 mOsm) to 319 mOsm or 344 mOsm in the lumbrical muscle cell of the mouse, resulted in a depolarization of the membrane potential (Vm) of 5.9 mV and 10.9 mV, respectively. In control medium, the blockers of chloride related cotransport bumetanide and furosemide, induced a hyperpolarization of −3.6 and −3.0 mV and prevented the depolarization due to hypertonicity. When bumetanide was added in hypertonic media Vm fully repolarized to control values. In a medium of 266 mOsm, the hyperpolarization by bumetanide was absent. At 344 mOsm the half‐maximal effective concentration (IC50) was 0.5 μm for bumetanide and 21 μm for furosemide. In solutions containing 1.25 mm sodium the depolarization by hypertonicity was reduced to 2.3 mV. Reducing chloride permeability, by anthracene 9 carboxylic acid (9‐AC) in 289 mOsm, induced a small but significant hyperpolarization of −2.6 mV. Increasing medium osmolality to 344 mOsm enlarged this hyperpolarization significantly to −7.6 mV. In a solution of 344 mOsm containing 100 μm ouabain, the bumetanide‐induced hyperpolarization of Vm was absent. The results indicate that a Na‐K‐2Cl cotransporter is present in mouse lumbrical muscle fibre and that its contribution to Vm is dependent on medium osmolality. British Journal of Pharmacology (1997) 120, 39–44; doi:

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

“…Also of interest in this experiment was the marked increase in net K + loss from barium treated muscle exposed to hypertonic medium. It is known that exposure to hypertonic medium results in depolarization of the sarcolemma that is associated with the net entry of Cl -into the cells [14,21]. Cellular shrinkage or membrane depolarization may have resulted in the transient opening of mechanosensitive or voltage-gated K + channels, allowing K + to flow down its chemical gradient.…”

“…First, a slowed rate of K + entry during periods of hyperosmotic stress may prevent the occurrence of a life-threatening hypokalemia during periods of increased K + transport into the cell via the NKCC and Na,K ATPase systems. Second, prevention of net K + flux during periods of hyperosmotic stress may be an important means of restoring cell volume and membrane electrogenicity, as the initial rapid influx of Cl -during such periods results in a transient membrane depolarization [14,21].…”

“…The perfusate was composed of washed bovine erythrocytes (hematocrit of 30±3%), dialyzed bovine serum albumin fraction 5 (Boehringer-Mannheim, Laval, Quebec; 70 g albumin/L plasma), a plasma ion solution and gassed with a humidified mixture of N 2 ] of 1.40±0.02. The perfusate also contained 1 mCi/L of binds to albumin [18], the free concentration of bumetanide in perfusate plasma was calculated to be 60 µM, similar to concentrations shown to elicit peak effects in skeletal muscle cells [19][20][21]. For experiments with 120 µM bumetanide, the infusion rate of the bumetanide stock solution was increased to 20 µl/min.…”

Isoprenaline-stimulated differential adrenergic response of K+ channels in skeletal muscle under hypokalaemic conditions

“…6) and that this depolarization is prevented when bumetanide is given prior to the hypertonic shock (second trace in Fig. 6) [38]. In addition, preincubation with Iso inhibited the depolarization caused by hypertonic solutions (third trace of Fig.…”

“…This transport can be modulated by hypertonicity of the medium and can be inhibited by the Na + /K + /2Cl cotransporter inhibitor bumetanide and by the chloride conductance inhibitor anthracene-9-carboxylic acid (9-AC). Both inhibitors cause membrane hyperpolarization [38]. An influence of protein phosphorylation on the Na + /K + /2Cl cotransporter has also been demonstrated in ferret erythrocytes [9] and on the chloride conductance in rabbit ventricular myocytes [15].…”