Related Experiment Videos
Immunologic identification of Na+,K(+)-ATPase isoforms in myocardium. Isoform change in deoxycorticosterone
K J Sweadner1, V L Herrera, S Amato
1Massachusetts General Hospital, Boston 02114.
Insights
This study investigates the expression of sodium-potassium adenosine triphosphatase (Na+,K(+)-ATPase) alpha subunit isoforms in various animal hearts. Findings reveal differential isoform expression correlating with cardiac glycoside sensitivity, crucial for understanding digitalis receptor diversity.
Area of Science:
- Cardiovascular Physiology
- Molecular Biology
- Pharmacology
Background:
- The catalytic (alpha) subunit of Na+,K(+)-ATPase exists in three isoforms with varying sensitivities to cardiac glycosides.
- Understanding digitalis receptor diversity is critical, particularly in ventricular myocardium.
Purpose of the Study:
- To investigate the expression patterns of Na+,K(+)-ATPase alpha subunit isoforms in the myocardium of different species.
- To correlate isoform expression with cardiac glycoside-response heterogeneity.
Main Methods:
- Utilized isoform-specific antibodies to detect Na+,K(+)-ATPase alpha subunit protein expression.
- Examined isoform distribution in rat, human, macaque, canine, sheep, and guinea pig hearts.
- Investigated the impact of hypertension and hypertrophy on isoform expression in rats.
Main Results:
- Rat ventricles co-express alpha 1 and alpha 2 isoforms, uniformly distributed in cardiomyocytes; hypertension reduced alpha 2 protein levels.
- Human hearts express all three isoforms (alpha 1, alpha 2, alpha 3); macaque hearts predominantly express alpha 1 and alpha 3.
- Canine hearts have alpha 1 and alpha 3, while sheep and guinea pig hearts only express alpha 1.
Conclusions:
- Na+,K(+)-ATPase alpha isoform expression is species-specific and can be modulated by physiological conditions like hypertension.
- Differential isoform expression provides a basis for understanding variations in cardiac glycoside sensitivity and digitalis receptor function.
Abstract:
There are three isoforms of the catalytic (alpha) subunit of the Na+,K(+)-ATPase, each derived from a different gene, that differ in their sensitivity to inhibition by cardiac glycosides. Antibodies specific for the three isoforms were used to study Na+,K(+)-ATPase isoform expression in ventricular myocardium, where an understanding of digitalis receptor diversity is most important. In the rat heart, there is simultaneous expression of two isoforms in adult ventricle, and immunofluorescence studies demonstrated that both isoforms are expressed uniformly in cardiomyocytes. Hypertension and hypertrophy have been reported to selectively depress alpha 2 isoform mRNA levels, and we show in the present study that alpha 2 protein levels were correspondingly depressed in rats made hypertensive by uninephrectomy and treatment with deoxycorticosterone acetate and a high-salt diet. In the human heart, where mRNA for all three alpha isoforms has been reported, we detected all three isoform proteins (alpha 1, alpha 2, and alpha 3). Two isoforms (alpha 1 and alpha 3) predominated in the macaque heart; dissection of the heart showed uniformity of isoform expression in different ventricular regions but markedly less alpha 3 in the atrium. Finally, isoform-specific antibodies were used to detect which alpha isoforms were expressed in the ventricles of several commonly used experimental animals to test the correlation of isoform expression with cardiac glycoside-response heterogeneity. Two isoforms (alpha 1 and alpha 3) were found in canine myocardium, whereas only one (alpha 1) was found in sheep and guinea pig. Expression of Na+,K(+)-ATPase isoforms can thus be readily followed and related to the physiology of the digitalis receptor.