Regulation of the Na⁺/K⁺-pump proteins in skeletal muscle: Acute effects of insulin on α2 distribution and muscle fibre-type specific expression of β subunits

Abstract

Insulin is a major anabolic hormone that plays a pivotal role in K⁺ homeostasis. A decrease in plasma K⁺ concentration is mentioned in the first reports of insulin effects on the whole organism. The hormone enhances active K⁺ uptake by extra-renal tissues, primarily muscle and liver (1). This response can be observed rapidly in isolated cell preparations such as excised muscle (2,3) and isolated hepatocytes (4). In isolated skeletal muscle, adipocytes and cardiocytes, addition of insulin results in a rapid hyperpolarization (5). This action has been mainly ascribed to a rapid stimulation of the Na⁺/K⁺-pump (6,7). In addition to incrementing K⁺ uptake and storage, the stimulation of the pump by insulin results in Na⁺ extrusion that is necessary to maintain low cytosolic levels of this cation, which would otherwise increase due to the simultaneous stimulation by the hormone of Na⁺-coupled amino acid uptake and Na⁺/H⁺ countertransport.