ATP depletion causes a reversible decrease in Na+ pump density in cultured ventricular myocytes

Abstract

To examine factors contributing to impaired K+ homeostasis induced by prolonged but sublethal ATP depletion, we subjected cultured chick ventricular myocytes to metabolic inhibition with 20 mM 2-deoxy-D-glucose plus 1 mM NaCN for 2 h and then allowed myocytes to recover for 5 days in medium containing 6% fetal calf serum (FCS) or in hormone-supplemented serum-free medium. We measured spontaneous contractions (with a video motion detector), K+ content, K+ uptake, membrane potential, and Na+ pump density ([3H]ouabain binding). Exposure to metabolic inhibition for 2 h caused an acute decrease in Na+ pump site density [8.2 +/- 1.1 to 3.8 +/- 0.8 (SE) pmol/mg protein; n = 9, P < 0.02]. Compared with control cells (no metabolic inhibition, cultured for 5 days in serum-free medium), Na+ pump density remained depressed in cells recovered from metabolic inhibition in serum-free medium (3.0 +/- 0.7 pmol/mg), and this was associated with persistently depressed K+ uptake (54% of control), K+ content (67% of control), and membrane depolarization (-19 +/- 2 mV), a significant decrease in cell number (79% of control), and failure to resume spontaneous contractions. Exposure of cells inhibited for 2 h to culture medium containing 6% FCS resulted in a return of Na+ pump site density toward normal levels by 5 days, associated with recovery of K+ uptake and K+ content, preservation of cell number, and resumption of contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential Na+–K+‐ATPase activity in rat lemniscal and non ‐ lemniscal auditory Thalami

“…If it can be assumed that both ventral and dorsal cell types express primarily the á3 isoform and that they have identical pump stoichiometry and turnover rate, then the density of pump molecules apparently becomes an important factor affecting the amplitude of the pump current. The membrane density of the Na¤-K¤-ATPase varies widely among different cell types and even in a given cell the membrane distribution of pump molecules can be highly heterogenous (Allen et al 1989;Cramb et al 1989;McGrail et al 1991;Ikenouchi, Zhao, McMillan, Hammond & Barry, 1993;Wang et al 1993). An example of such functional differential distribution has been described recently in guinea-pig heart where the atrial and ventricular myocytes are reported to contain different amounts of pump molecules and, as a result, exhibited different contractile force in response to ouabain (Wang et al 1993).…”

Molecular Control of Cardiac Sodium Homeostasis in Health and Disease

“…In this context we describe relevant results using giant excised cardiac patches to analyze Na/K pump currents. Additionally, it is suggested that Na/K pumps become inhibited during ATP depletion by mechanisms that are not simply related to substrate binding 32,44,45 . A still more complex scenario is suggested by evidence that phosphorylation of phospholemman, which is thought to regulate cardiac pumps, has a strong stimulatory effect on Na/K pumps that opposes effects of the pump inhibitor induced by ischemia 46 …”

Cardiomyocytes from postinfarction failing rat hearts have improved ischemia tolerance

“…Increased intracellular Na ϩ is suggested as a major cause of NCX to run in Ca 2ϩ influx mode and causes Ca 2ϩ accumulation in the cardiomyocytes during reperfusion. The possible mechanisms for the increase in intracellular Na ϩ during ischemia (53) are decreased Na ϩ -K ϩ -ATPase activity (1,17,18,29,32), tissue acidosis, and increased tissue CO 2 (8,49) with increased Na ϩ /H ϩ exchange activity (1,20,23,24,33,54) and Na ϩ entry via Na ϩ channels and possibly other cation channels. The markedly larger inhibitory effect of ranolazine, the inhibitor of late Na ϩ current (50), on the increase in exchangeable Ca 2ϩ and the increase in LD release in sham cells than in CHF cells after reoxygenation indicates that differences between CHF and sham cells in late Na ϩ current during hypoxia might explain the differences in Na ϩ uptake during hypoxia and the differences in ischemia tolerance observed in this study.…”