A 23Na-NMR study on cation transport systems in a patient with hypokalemic periodic paralysis.
Erythrocytes from a patient with hypokalemic periodic paralysis (HPP) have been studied, in order to investigate the presence of alterations of membrane cation active transport systems. An original 23Na-NMR method has been used, capable of evaluating quantitatively the Na+ efflux due to the Na+/K+/Cl- cotransport. This method uses a loading system to increase internal cellular Na+ concentration: in the patient with HPP both the internal Na+ concentration after loading and the Na+/K+/Cl- cotransport activity were decreased in comparison to the controls. Our data seem to confirm that the fall of K+ serum levels during attacks in HPP must be ascribed to a shift of K+ from extra- to intracellular compartment (with consequent changes in the fibrocellular membrane polarity), due to an alteration of membrane cation transport system: which does not only consist in a hyperactivity of Na+/K+ ATPase (already described by other AA.), but also in a "secondary" decreased K+ efflux driven by the cotransport. The decrease of cotransport activity may be considered as "compensatory" (in fact, the intracellular Na+ content is normal), since this transport system can work as a kind of "emergency" system that can "help" the ATPase-dependent pump in extruding any excess of cell Na+ content, or can be depressed by any decrease of this value, caused by an hyperactivity of the Na+/K+ ATPase. The decreased cotransport activity results in a powerful contribution to the increase of intracellular potassium due to the hyperactivity of the Na+/K+ pump. This method could supply a useful diagnostic marker in all uncertain cases.
Istituto di I Clinica Medica, Università La Sapienza, Roma.
M
M
Cacciafesta
I
I
Cammarella
R
R
Ruggeri
M A
MA
Germani
A R
AR
Soldo
A
A
Musca
D000328:Adult; D001693:Biological Transport, Active; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D007008:Hypokalemia / Q000097:blood / Q000175:diagnosis*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D009123:Muscle Hypotonia / Q000097:blood / Q000175:diagnosis; D010243:Paralysis / Q000097:blood / Q000175:diagnosis*; D010507:Periodicity; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood*; D012979:Sodium Radioisotopes; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood
D012979:Sodium Radioisotopes; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium