Cyclosporine and FK506 differentially regulate the sarcolemmal Na(+)-K(+) pump

Cyclosporine A (CsA) and FK506, important immunosuppressants, have been shown to inhibit the enzymatic equivalent of the Na(+)-K(+) pump (Na(+), K(+)-ATPase) in renal tissue. A similar effect in the heart may contribute to the adverse effects of these agents that include calcification, contractile dysfunction, and altered calcium handling. However, inhibition of the pump has not been demonstrated in cardiac myocytes. We isolated single ventricular myocytes from control rabbits and from rabbits administered CsA or FK506 for 1 week. Na(+)-K(+) pump current (I(p)) was measured using the whole-cell patch-clamp technique. When patch pipettes contained Na(+) in a concentration ([Na](pip)) near physiological intracellular levels mean I(p) of cardiac myocytes from rabbits with serum CsA levels within the therapeutic range was significantly lower than mean I(p) of cardiac myocytes from controls. Treatment had no effect on I(p) measured using a [Na](pip) expected to nearly saturate intracellular binding sites. The CsA-induced inhibition of I(p) was dependent on the K(+) concentration in pipette solutions. Mean I(p) in myocytes from rabbits with serum levels of FK506 within the therapeutic range was similar to mean I(p) in myocytes from controls, whereas FK506 in a dose inducing serum levels severalfold above the therapeutic range caused significant pump inhibition. Using ion-sensitive microelectrodes we showed the intracellular Na(+) activity in papillary muscles isolated from rabbits treated with CsA was significantly higher than in papillary muscles from control rabbits, indicating that CsA causes pump inhibition in intact myocytes with a physiological intracellular milieu.

Hyperaldosteronemia in rabbits inhibits the cardiac sarcolemmal Na(+)-K(+) pump

Aldosterone upregulates the Na(+)-K(+) pump in kidney and colon, classical target organs for the hormone. An effect on pump function in the heart is not firmly established. Because the myocardium contains mineralocorticoid receptors, we examined whether aldosterone has an effect on Na(+)-K(+) pump function in cardiac myocytes. Myocytes were isolated from rabbits given aldosterone via osmotic minipumps and from controls. Electrogenic Na(+)-K(+) pump current, arising from the 3:2 Na(+):K(+) exchange ratio, was measured in single myocytes using the whole-cell patch clamp technique. Treatment with aldosterone induced a decrease in pump current measured when myocytes were dialyzed with patch pipette solution containing Na(+) in a concentration of 10 mmol/L, whereas there was no effect measured when the solution contained 80 mmol/L Na(+). Aldosterone had no effect on myocardial Na(+)-K(+) pump concentration evaluated by vanadate-facilitated [(3)H]ouabain binding or by K(+)-dependent paranitrophenylphosphatase activity in crude homogenates. Aldosterone induced an increase in intracellular Na(+) activity. The aldosterone-induced decrease in pump current and increased intracellular Na(+) were prevented by cotreatment with the mineralocorticoid receptor antagonist spironolactone. Our results indicate that hyperaldosteronemia decreases the apparent Na(+) affinity of the Na(+)-K(+) pump, whereas it has no effect on maximal pump capacity.

Variability of the Holt-Oram syndrome in Saudi individuals

We studied three families in which patients with the Holt-Oram syndrome (HOS) had various skeletal abnormalities and congenital heart defects. Two patients had absent thumbs and first metacarpals, hypoplastic radii, and atrial and ventricular septal defects. Patient 2 had pulmonary stenosis, an atrial septal defect, and triphalangeal thumbs. A sister had atrial septal defect and abnormalities of the thumbs; two brothers had abnormalities of the thumbs. The mother had unilateral defect of the thumb with a normal heart. The third patient had tetralogy of Fallot and hypoplastic pulmonary artery. In two families the HOS appeared to be the result of new mutations; in one it was transmitted as an autosomal dominant trait.

Thomas G. Orr Memorial Lecture. Cardiovascular surgery in Saudi Arabia

A program in cardiovascular surgery from Baylor College of Medicine was transplanted halfway around the world to the Kingdom of Saudi Arabia, providing services with results similar to those obtained in more medically advanced areas of the world. In order to do this, however, numerous support services must be in place and functioning efficiently, and there must be a cooperative spirit on the part of all concerned. In this manner it has been possible not only to provide cardiovascular service to the Kingdom, but also to establish a bidirectional training program. It is intended that eventually this program of cardiovascular surgery will be conducted by Saudi nationals.