Neural regulation on the active sodium-potassium transport in hypokalaemic rat skeletal muscles

Long-Term Effects of Botulinum Toxin Complex Type A Injection on Mechano- and Metabo-Sensitive Afferent Fibers Originating from Gastrocnemius Muscle

The aim of the present study was to investigate long term effects of motor denervation by botulinum toxin complex type A (BoNT/A) from Clostridium Botulinum, on the afferent fibers originating from the gastrocnemius muscle of rats. Animals were divided in 2 experimental groups: 1) untreated animals acting as control and 2) treated animals in which the toxin was injected in the left muscle, the latter being itself divided into 3 subgroups according to their locomotor recovery with the help of a test based on footprint measurements of walking rats: i) no recovery (B0), ii) 50% recovery (B50) and iii) full recovery (B100). Then, muscle properties, metabosensitive afferent fiber responses to potassium chloride (KCl) and lactic acid injections and Electrically-Induced Fatigue (EIF), and mechanosensitive responses to tendon vibrations were measured. At the end of the experiment, rats were killed and the toxin injected muscles were weighted. After toxin injection, we observed a complete paralysis associated to a loss of force to muscle stimulation and a significant muscle atrophy, and a return to baseline when the animals recover. The response to fatigue was only decreased in the B0 group. The responses to KCl injections were only altered in the B100 groups while responses to lactic acid were altered in the 3 injected groups. Finally, our results indicated that neurotoxin altered the biphasic pattern of response of the mechanosensitive fiber to tendon vibrations in the B0 and B50 groups. These results indicated that neurotoxin injection induces muscle afferent activity alterations that persist and even worsen when the muscle has recovered his motor activity.

Potassium depletion in a healthy north-eastern Thai population: No association with tubulo-interstitial injury

Potassium depletion prevails among the healthy population of north-east Thailand, as well as among patients with certain metabolic disorders such as upper urinary tract stones, the sudden unexplained death syndrome, distal renal tubular acidosis and hypokalaemic periodic paralysis. However, definite proof of the relationship of potassium depletion and these metabolic disorders is lacking. We prospectively studied muscle and kidney potassium content including renal tissue pathology in three groups of healthy adult Thai subjects who died of vehicular accidents. Group 1 (n = 24) were Bangkok city dwellers; groups 2 (n = 10) and 3 (n = 22) lived in north-eastern Thailand in the metropolitan area and in the villages, respectively. The muscle potassium content of group 1 (338.5 +/- 9.6 mEq/kg dry weight (DW)) were similar to group 2 (307.9 +/- 11.9 mEq/kg DW), but was greater than group 3 (295.4 +/- 9.1 mEq/kg DW; P < 0.01). The kidney potassium content of group 1 (208.6 +/- 7.8 mEq/kg DW) was significantly higher than group 3 (175.9 +/- 6.3 mEq/kg DW, P < 0.05). In group 3, the muscle potassium correlated linearly with the kidney potassium (r = 0.455, P = 0.33). None of the group 3 patients had renal histopathological change compatible with a diagnosis of focal or diffuse interstitial nephritis. This study confirms that potassium depletion is common among healthy rural dwellers in north-east Thailand. This deficit was probably chronic. However, there was minimal renal tubulo-interstitial change.

On the trail of potassium in heat injury

In both classical and exertional heatstroke and in various animal models of human heat injury, clinical manifestations have included observations of normokalemia, hyperkalemia, and hypokalemia. This review attempts to address these observations as well as the role of potassium and potassium depletion in heat injury with an emphasis on the integration of information from the level of transmembrane potassium transport mechanisms to systems physiology. Under moderate conditions of passive heat exposure or exercise in the heat, the adaptive capacity of the Na-K pump (Na+-K+ ATPase activity) and cotransport mechanisms can ordinarily accommodate the attendant increased efflux of intracellular K+ and influx of extracellular Na+ to maintain ionic equilibrium. Several factors affecting transmembrane K+ kinetics include protracted K+ deficiency, extreme hyperthermia, dehydration, and excessive exertion. These could elicit reduced membrane potentials and conductance, futile cycling of the Na-K pump with concomitant energy depletion and greatly increased metabolic heat production, reduced arteriolar vasodilation, altered neurotransmitter release, or cell swelling, each of which could contribute to the pathophysiology of heat injury. This review represents a preliminary attempt to link transmembrane K+ pathophysiology with clinical heat injury.

Changes of intracellular electrolyte contents in rat skeletal muscle during body suspension

The CNS-mediated inhibition of active Na(+)-K+ transport in both "type S" muscle, soleus (SOL), and "type FF" muscle, extensor digitorum longus (EDL) was investigated in rats suspended horizontally. Plasma Na+ and K+ contents did not change during the suspension period. The relative wet weight of SOL decreased more than that of EDL by suspension. There was significant intracellular Na+ accumulation and K+ loss in both SOL and diaphragm of suspended rats. However, cerebrum, cerebellum, medulla oblongate, ventricle, liver, pancreas, kidney, intestine, aorta and EDL were spared from the intracellular Na+ accumulation and K+ loss. Sciatic nerve sectioning or cervical spinal cord transection recovered the Na+ and K+ contents in the SOL of suspended rats. The results indicate the existence of neural inhibition of the active Na(+)-K+ transport in skeletal muscle of the suspended rats.

Effects of catecholamines on plasma potassium: the role of alpha- and beta-adrenoceptors

The sympathetic nervous system plays an important role in the control of plasma potassium levels. Administration of adrenaline or noradrenaline evokes, in the majority of mammal species a dual response: first a short transient hyperkalaemia, followed by a maintained hypokalaemia. Alpha 1- and alpha 2-adrenoceptors mediate the initial hyperkalaemia through the activation of hepatic Ca(2+)-dependent-K(+)-channels. Stimulation of beta 1- and beta 2-adrenoceptors induces the late hypokalaemia by stimulation of skeletal muscle Na(+)-K(+)-ATPase. Beta 3-adrenoceptor stimulation may also have an effect on plasma potassium control since administration of selective beta 3-adrenoceptor agonists induces a decrease in plasma potassium. The simultaneous infusion of phenyleprine (alpha-adrenoceptor agonist) and isoprenaline (beta-adrenoceptor agonist) increases plasma potassium levels: this effect is several times larger than the algebric summation of the changes in plasma potassium when each agent is infused separately, thus suggesting potentiation. The physiological (changes in cell volume and function secondary to changes in ion fluxes) and clinical implications (pathophysiological conditions with hypo or hyperkalaemia, hyperkalaemic periodic paralysis, ventricular arrythmias) of these findings are discussed.

Appearance of alpha 1-adrenergic receptors in soleus muscles from SHR

The depressed functional capabilities of spontaneously hypertensive rat (SHR) muscles, reported previously (Exp. Neurol. 95: 249-264, 1987), may reflect a decrease in muscle responsiveness to catecholamines occurring as a consequence of exposure to the elevated level of plasma catecholamines in SHR. Responsiveness to applied catecholamines was determined in SHR and Wistar-Kyoto rat (WKY) soleus by measuring muscle resting membrane potentials (RMP) in vitro. Epinephrine (10(-6) M) produced a similar membrane hyperpolarization in SHR and WKY fibers. Pretreatment with the beta-antagonist propranolol completely blocked the epinephrine-induced hyperpolarization in WKY, but not in SHR. SHR soleii from both young and old rats contained a population of alpha 1-adrenergic receptors also associated with membrane hyperpolarization. The alpha-receptors appeared to be associated with a ligand-gated Ca(2+)-influx pathway, since the alpha-agonist-induced membrane hyperpolarization required the presence of Ca2+ in the extracellular medium. The alpha-induced hyperpolarization was also blocked by apamin, a derivative of bee venom which blocks a Ca(2+)-activated K(+)-efflux pathway in a variety of tissues. The possible role of these novel alpha-receptors in skeletal muscle function, and their relationship to the development of hypertension, is uncertain.

Change of intracellular K+ activity in rat soleus muscle during hypokalemia

The relationship between intracellular total K+ concentration [( K]i) as determined by a flame spectrophotometer and intracellular K+ activity (aKi) as determined by an ion-selective microelectrode was studied in soleus muscle of rats on a diet deficient in K+ for 40 days. [K]i began to fall immediately from the initial stage of hypokalemia, while aKi was well-maintained for 15 days. Then, aKi decreased gradually. The measured resting potential (Em) hyperpolarized beyond the EK was calculated from aKi in hypokalemic rat muscle from day 20 to 40. A rapid increase in aKi occurred over 3 hours in soleus muscle of hypokalemic rats for 5 to 6 weeks. It was concluded that the bound intracellular K+ acts as a buffer for aKi in hypokalemic rat muscle, that Em exceeds EK because the Na+-K+ pump is stimulated by increased [Na]i and that the increase in aKi after denervation is due to the removal of a Na+-K+ pump inhibitor normally released from nerve ending.

Hypokalemic periodic paralysis with unusual responses to acetazolamide and sympathomimetics

Five members in three generations of a family were affected by an illness that had many clinical features of the hypokalemic form of periodic paralysis (HPP). The serum potassium was either moderately reduced or normal during attacks, and there was no evidence of myotonia or cold-intolerance. All of the patients improved to a variable degree with oral potassium supplements, and 3 responded favorably to triamterene. The usually beneficial drug acetazolamide, however, invariably caused weakness in these patients, an effect previously described in only one other family with HPP. In addition, amphetamine-like sympathomimetic drugs effectively aborted or prevented paralysis in several members. Muscle biopsy in two patients revealed some unusual features, and electromyography showed myopathic potentials. There was no evidence of diabetes. The urine electrolyte concentrations during glucose tolerance tests, however, were different from those previously reported in HPP. This family may represent a variant form of HPP.

Active sodium-potassium transports in skeletal muscles of deoxycorticosterone hypertensive rats

CNS-induced suppressions of active Na+, K+ transport was investigated in both 'tonic' muscles, soleus (SOL), and 'twitch' muscle, extensor digitorum longus (EDL) of deoxycorticosterone acetate (DOCA) hypertensive rats. There was a marked K+ loss and Na+ accumulation in the skeletal and smooth muscles of DOCA hypertensive rats. The cellular K+ loss was in the order of SOL greater than EDL greater than diaphragm greater than intestine greater than aorta. However, liver, kidney and CNS organs such as cerebrum, cerebellum and medulla oblongata were spared from this K+ fall. Sciatic nerve sectioning or cervical transection activated the active Na+, K+ transport in SOL during DOCA hypertension but inhibited further the pump activity in EDL. The application of tetrodotoxin on the sciatic nerve also activated the Na+, K+ transport in SOL but inhibited the transport in EDL. The facilitatory effect of denervation on the pump activity in SOL was abolished by pretreatment with ouabain. Injection of curare had no effect on Na+ and K+ contents in both SOL and EDL. These results indicate that the CNS is involved differently on the neural regulations of the active Na+, K+ transport systems in SOL and EDL of DOCA hypertensive rats.

Decrease in force potentiation and appearance of alpha-adrenergic mediated contracture in aging rat skeletal muscle

The effect of increasing age on contractile performance and catecholamine receptor activity was investigated in a distal, predominantly fast twitch oxidative glycolytic (FOG) muscle from the plantar surface of the rat hindfoot. The ability of the flexor digitorum brevis (FDB), isolated from anesthetized rats and maintained in vitro, to undergo post-tetanic potentiation and a staircase response declined with age. Potentiation following repetitive stimulation was reduced by 50% in 2 year old rats and eliminated in 3 year old animals. The rate of muscle fatigue during intermittent tetanic stimulation also increased in aging muscles. FDB, regardless of age, did not develop a positive inotropic response to 10(-6) M epinephrine applied in vitro, but 3 year old FDB generated a prolonged contracture. Contracture tension was approximately 25% of twitch tension and was maintained for 2-10 min in the continued presence of catecholamine. Contractures were eliminated by pretreatment with alpha-adrenergic antagonists or by removing Ca2+ from the bathing medium. In addition to decreased contractile capacity, aging muscles acquire a population of alpha-adrenergic receptors which may underlie some of the metabolic and structural changes associated with increasing age.

Decline of isometric force and fatigue resistance in skeletal muscles from spontaneously hypertensive rats

Skeletal muscles from 6- to 7-month-old male spontaneously hypertensive rats showed a decrease in functional capacity compared with muscles from age-matched normotensive Wistar-Kyoto rats. Predominantly slow-twitch, oxidative soleus muscles developed less force (normalized to muscle wet weight) and were less resistant to fatigue. Heterogeneous, but largely fast-twitch, oxidative-glycolytic medial gastrocnemius muscles generated less force, were smaller in size (normalized to body weight), and did not demonstrate the same degree of stimulation-associated potentiation (staircase effect) as did the medial gastrocnemius of the normotensive rats. The reduced endurance of the soleus of hypertensive rats was not associated with either fiber redifferentiation or capillary "rarification," and the majority of the decline in force with time could not be attributed to impaired neuromuscular transmission. The decrease in muscle capacity in the spontaneously hypertensive rat, thus, appears to be the result of adaptive changes localized in the muscle cells themselves. The adaptive changes, regardless of site, have a pronounced negative effect on muscle function, and could significantly influence motor performance and antihypertensive therapy.

Comparison of red and white muscle wet weight changed by age, denervation and morbid states

[Na]i, [K]i and wet weight of the extensor digitrum longus (EDL) and soleus (SOL) muscles of 9- and 52-week-old rats were measured for 7 days after sectioning of the sciatic nerve. The changes in wet weight of the EDL and SOL muscles of rats over 52 weeks and those of morbid state rats were also measured. There was no significant difference in wet weights between the EDL and SOL muscles in infant rats, but the EDL muscle became much heavier than the SOL muscle with aging. The decrease in rate of growth of wet weight of the EDL and SOL muscles caused by denervation, was greater in young rats than in mature rats. In addition, the rate of decrease was greater in the SOL muscles than in the EDL muscles in both young and mature rats. The [Na]i increased while [K]i was decreased by denervation, and the net Na+ increase and the net K+ loss were greater in young rats than in mature rats. The changing rate was more remarkable in the EDL muscles than in the SOL muscles throughout the aging process. During DOCA treatment over 4 weeks, the decrease of muscle wet weight was greater in the EDL muscles. The mechanisms which serve to maintain normal muscle wet weight in the SOL muscle after denervation or treatment with DOCA, were discussed.

Hypothalamic regulation of sodium-potassium pump activity in skeletal muscle

The suppression of active Na+-K+ transport in rat skeletal muscle during hypokalemia was counteracted by bilateral electrolytic lesion of the ventromedial hypothalamic nucleus. This reversal effect was unaffected even after pancreatectomy or adrenalectomy. The anomalous electrolyte content in hypokalemic rat muscles was aggravated by lesion of the dorsomedial hypothalamic nucleus and of the anterior hypothalamus. The results indicate that the hypothalamus is involved in the regulation of the Na+-K+ transport system in skeletal muscle during hypokalemia.

Hypokalemia modulates alpha- and beta-adrenoceptor bindings in rat skeletal muscle

Changes in the population of adrenergic alpha- and beta-receptors were examined in rat soleus muscles during hypokalemia by their direct determination using radiolabeled ligands. Only beta-adrenoceptors were detected in the normal rat muscles. Hypokalemia led to a pronounced decrease in beta-adrenoceptors, the number of [3H]DHA binding sites, by 50%, as compared with that in the normal rats. There was a genesis of alpha 1-adrenoceptors in hypokalemic rat muscles, since the competitive potency of adrenergic drugs against [3H]prazosin binding was in the order prazosin much greater than phentolamine greater than (+/-)-noradrenaline greater than yohimbine much greater than (+/-)-isoproterenol. The reduction of [3H]DHA binding sites was accompanied by an increase of an approximately equal amount in high-affinity [3H]prazosin binding sites. The Kd determined by kinetic analysis of [3H]prazosin binding was calculated from the ratio K-1/K1 that gave a value of 3.05 nM, which generally agreed with the 1.83 nM determined by saturation experiments (Scatchard plot). This phenomenon of a reduction in the beta-adrenoceptors and the occurrence of alpha 1-adrenoceptors in muscles during hypokalemia is discussed. alpha- and beta-adrenoceptors on soleus muscle membrane may play important but opposite roles in modulating potassium release from the muscle cells.

The electrogenic Na-pump and spontaneous contraction of the hypokalemic rat duodenum

The effects of the electrogenic Na-pump on spontaneous contraction in the isolated, longitudinal muscle of the duodenum of rats which had been on a potassium-deficient diet for 7 weeks, have been investigated. Intracellular levels of Na+ are increased by this diet. The spontaneous contraction of the duodenal muscle was stopped, transiently, by 0.5 to 120 mM-K+ Krebs solution. The period of decrease of tone and amplitude occurring immediately after adding K+ was shortened when the external K+ concentration ([K]o) was increased from 0.5 to 120 mM. The decrease in tone and amplitude induced by K+ was abolished by exposure of the tissue to 0 mM [K]o, by exposure to a temperature below 14 degrees C, and in the presence of ouabain (3 X 10(-5)-10(-4) M). The spontaneous contraction of 'Na-rich' duodenum in bathing medium containing 15 mM K+ and following inhibition of the electrogenic Na-pump with cooling or ouabain was much the same as in the duodenum from rats fed balanced diets: i.e., increase of contractile tone immediately after adding K+. To activate the Na-pump in 'Na-rich' duodenum, the external K+ could be replaced by Rb+, Cs+, NH4+ and Tl3+. The effectiveness was in the order K+ greater than Rb+ greater than Cs+ greater than NH4+ greater than Tl3+. The possible existence of a neuronal or hormonal inhibitory mechanism affecting the active Na-K transport in rat smooth muscle in situ, under conditions of hypokalemia, is discussed.

Effects of hypothalamic lesions on active sodium-potassium transport in the extensor digitorum longus muscles of hypokalemic rat

The CNS-induced suppression on muscle Na+-K+ pump was studied in "twitch" muscle, extensor digitorum longus (EDL), of hypokalemic rats which were fed a K+ deficient diet for several weeks. Peripheral nerve section or bilateral lesion of the ventromedial hypothalamic nucleus had no effect on the Na+ and K+ contents in EDL of hypokalemic rats. However, lesions of the paraventricular nucleus caused the net Na+ loss and the net K+ uptake in the muscles. Lesions in either the dorsomedial nucleus or anterior hypothalamus also caused significant net K+ uptake but the net Na+ loss was not significant. The results were compared with those of "tonic" muscle, soleus, reported previously.

Impairment of extrarenal potassium disposal by alpha-adrenergic stimulation

Since beta-adrenergic stimulation enhances extrarenal potassium uptake, we postulated an opposite effect of the alpha-adrenergic nervous system. Seven healthy subjects were given intravenous potassium chloride (0.5 mmol per kilogram of body weight), in the presence and absence of the alpha-agonist phenylephrine. After potassium chloride alone, the potassium level rose to 0.64 +/- 0.03 mmol (mean +/- S.E.M.); phenylephrine augmented the rise (0.93 +/- 0.09 mmol, P less than 0.025) and prolonged it, without changing urinary potassium excretion. Subsequent administration of potassium and phenylephrine together with the alpha-antagonist phentolamine blocked the rise in the potassium level due to phenylephrine and shortened the duration of elevation, again without affecting urinary potassium excretion. No changes in plasma renin and aldosterone levels or in serum insulin concentrations occurred, to account for these findings. Stimulation of alpha-adrenergic receptors impairs extrarenal disposal of an acute potassium load--the opposite effect of beta-adrenergic stimulation. The alpha-adrenergic effect may act to preserve a normal serum potassium level or may contribute to hyperkalemia under certain circumstances, such as vigorous exercise.