Enhanced Na+/H+ exchange in Cushing's syndrome reflects functional hypermineralocorticoidism.

Background: Patients with Cushing's syndrome exhibit a bimodal distribution of maximal rates of the erythrocyte amiloride-sensitive Na+/H+ exchange (NHE). Enhanced erythrocyte NHE has recently been found in patients with primary aldosteronism.

Objective: To test the hypothesis that occult hypermineralocorticoidism in a subset of patients with Cushing's syndrome is responsible for the greater than normal NHE.

Rhabdomyolysis associated with clozapine treatment in a patient with decreased calcium-dependent potassium permeability of cell membranes.

A 21-year-old patient developed rhabdomyolysis during his nineteenth week of treatment with clozapine for drug-resistant schizophrenia. No risk factors for rhabdomyolysis were found, but the calcium-dependent potassium efflux, normally responsible for membrane hyperpolarization and muscle refractoriness, was severely decreased in the patient's red blood cells. Clozapine is speculated to cause rhabdomyolysis in patients with defective calcium-activated K+ channels.

Xiphodynia masking acute myocardial infarction: a diagnostic cul-de-sac.

A 52-year-old hypertensive woman is described in whom a clinically evident diagnosis of xiphodynia, the painful xiphoid process, complicated the diagnosis of impending myocardial infarction. The authors suggest that xiphodynia be considered a second-line assumption after more dangerous conditions have been thoroughly ruled out.

Enhanced erythrocyte Na+/H+ exchange predicts diabetic nephropathy in patients with IDDM.

Diabetic nephropathy develops in a subset of patients with an apparently hereditary predisposition. Microalbuminuria and elevated arterial pressure have been proposed as predictors of nephropathy but both appear when renal damage is impending. Enhanced sodium-hydrogen exchange in the cell membranes of diabetic patients is an early marker of diabetic nephropathy but its predictive value has not been assessed.

Membrane ion transport in Bartter's syndrome: evidence for a new syndrome subtype.

Fifteen patients with Bartter's syndrome (hyponatremic hypochloremic hypokalemic metabolic alkalosis) were compared with 15 healthy volunteers. Red blood cell Na+/H+ and Cl-/HCO3- exchanges were enhanced in all patients with Bartter's syndrome. In calciuric normomagnesemic patients, sensitive to nonsteroidal anti-inflammatory drugs (classic Bartter's syndrome), red blood cell Na+,K+,2Cl- cotransport was markedly reduced, calcium-dependent K+ permeability was moderately increased, and up to 60% of sodium permeability was represented by cAMP-activated fraction (presumably human analog of beta-isoform of Na+/H+ exchange).