Mechanism of muscular paralysis by insulin with particular reference to familial periodic paralysis

Disruption of Sur2-containing K(ATP) channels enhances insulin-stimulated glucose uptake in skeletal muscle

ATP-sensitive potassium channels (K(ATP)) are involved in a diverse array of physiologic functions including protection of tissue against ischemic insult, regulation of vascular tone, and modulation of insulin secretion. To improve our understanding of the role of K(ATP) in these processes, we used a gene-targeting strategy to generate mice with a disruption in the muscle-specific K(ATP) regulatory subunit, SUR2. Insertional mutagenesis of the Sur2 locus generated homozygous null (Sur2(-/-)) mice and heterozygote (Sur2(+/-)) mice that are viable and phenotypically similar to their wild-type littermates to 6 weeks of age despite, respectively, half or no SUR2 mRNA expression or channel activity in skeletal muscle or heart. Sur2(-/-) animals had lower fasting and fed serum glucose, exhibited improved glucose tolerance during a glucose tolerance test, and demonstrated a more rapid and severe hypoglycemia after administration of insulin. Enhanced glucose use was also observed during in vivo hyperinsulinemic euglycemic clamp studies during which Sur2(-/-) mice required a greater glucose infusion rate to maintain a target blood glucose level. Enhanced insulin action was intrinsic to the skeletal muscle, as in vitro insulin-stimulated glucose transport was 1.5-fold greater in Sur2(-/-) muscle than in wild type. Thus, membrane excitability and K(ATP) activity, to our knowledge, seem to be new components of the insulin-stimulated glucose uptake mechanism, suggesting possible future therapeutic approaches for individuals suffering from diabetes mellitus.

Relationship between ionic surroundings and insulin actions on glucose transport and Na,K-pump in muscles

1. It is well known that insulin has various effects on glucose transport and the Na,K-pump in muscles. It is also known to have some effects on the membrane potential--in general, insulin induces a hyperpolarization of the membrane in muscles. Furthermore, it is suggested that the actions of insulin are modified by changes in ionic surroundings. 2. In this review article, the actions of ionic surroundings and insulin on glucose transport in muscles are discussed; in particular, the effects of changes in extracellular and/or intracellular concentrations of Na, K, Ca and H ions will be mentioned. 3. The actions of ionic surroundings and insulin on the Na,K-pump in muscles are discussed; in particular, the effects of changes in extracellular an/or intracellular concentrations of Na, K, Ca and H ions will be examined. 4. The relationship between the actions of ionic surroundings and insulin are discussed. 5. In particular, the effects of changes in ionic surroundings on the insulin-induced hyperpolarization of the membrane are discussed by relating it to the Na,K-pump function. The relationship between the insulin-induced change in membrane potential and glucose transport will be also mentioned.

Insulin does not hyperpolarize rat muscle by means of a ouabain-inhibitable process

Experiments were designed to test the hypothesis that insulin-induced hyperpolarization of rat skeletal muscle is mediated by stimulation of a ouabain-inhibitable electrogenic pump. Parallel experiments were carried out on rat caudofemoralis with isoproterenol, known to hyperpolarize rat skeletal muscle by stimulation of such a pump. Ouabain (10(-5) M) completely inhibited isoproterenol-induced hyperpolarization within 15 min but had no effect on half-maximal insulin-induced hyperpolarization. Ouabain (10(-6) M) inhibited isoproterenol effect by 60% during a period of 5-15 min. Ouabain (10(-4) M) had no effect on insulin-induced hyperpolarization within 10 min but depolarized during the next 10 min. In a separate series of studies in rat extensor digitorum longus muscle, 10(-5) M ouabain increased intracellular Na+ within 14 min. It is concluded that in rat caudofemoralis muscle, insulin-induced hyperpolarization is not mediated by a ouabain-inhibitable electrogenic pump.

Rapid hyperpolarization of rat skeletal muscle induced by insulin

It has been proposed that the increase produced by insulin in electrical potential differences across membranes of target cells may be a mechanism by which the cell surface insulin-receptor complex causes at least some of the metabolic effects of insulin. If insulin-induced hyperpolarization is a transducer of common effector responses it must precede those responses. The problem has not been addressed previously, so that rapid responses to insulin have not been sought. Two methods were used. In one method, the bathing solution was changed rapidly so as to include insulin in supramaximal concentrations, and a series of measurements of membrane potentials. Er, were made. Insulin hyperpolarized by 9.4 mV within 1 min. In the other method, nanoliter amounts of highly concentrated insulin solution were ejected from a micropipette onto the surface of an impaled muscle fiber. In 21 out of 32 insulin injections, hyperpolarization occurred with 1 s; in 11 control injections there was no change. This is the most rapid response to insulin yet reported, and is consistent with the hypothesis that insulin-induced hyperpolarization may transduce effector responses.

Endogenous insulin fluctuations during glucose-induced paralysis in patients with familial periodic hypokalemia

Endogenous insulin production in patients with familial periodic hypokalemia has not previously been studied during induced attacks. The serum insulin, serum potassium, and blood glucose concentrations were measured in six patients with familial periodic hypokalemia during six attacks of paralysis induced by long-lasting glucose stimulation. The same parameters were measured in four normal subjects under the same conditions. There was no difference in insulin response or in blood glucose between the two groups. Basal insulin levels showed no difference. There was no correlation between the occurrence of the attack and the serum insulin level in the patients. All the patients responded by severe paralysis and hypokalemia.

The effects of potassium ions and denervation on protein synthesis and the transport of amino acids in muscle

1. The effects of varying concentrations of K(+) during incubation, of denervation and of various drugs on the accumulation of (14)C-labelled amino acids, their incorporation into protein and the stimulation of these processes by insulin in rat diaphragm preparations were studied. 2. The accumulation of glycine and aminoisobutyrate and incorporation of glycine into protein was less in tissue incubated in K(+)-free buffer or 20mm-K(+) than with 5-10mm-K(+). Incorporation of leucine was unaffected. 3. Incorporation into protein of amino acids by diaphragm that had been denervated 3 days previously was elevated. Accumulation of both glycine and aminoisobutyrate was also raised but that of phenylalanine was unaffected. 4. Accumulation of glycine by diaphragm and extensor digitorum longus muscle was decreased by a number of agents including cocaine and mepyramine. 5. The stimulation of incorporation by insulin was unaffected by changes in K(+) or in the presence of cocaine and mepyramine. Denervated tissue was markedly less responsive to insulin than its control. 6. The results are discussed in the context of the relation of amino acid accumulation to operation of the Na(+) pump and the influence of insulin thereon.