Distinction between the two basic mechanisms of cation transport in the cardiac Na sup + -Ca sup + exchange system

Journal Article · Tue Mar 13 00:00:00 EST 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00462a001· OSTI ID:6073988

Khananshvili, D ^[1]

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1. Weizmann Institute of Science (Israel)

In order to distinguish between the Ping-Pong and sequential mechanisms of cation transport in the cardiac Na{sup +}-Ca{sup 2+} exchange system, the initial rates of the Na{sub i}-dependent {sup 45}Ca uptake were measured in reconstituted proteoliposomes, loaded with a Ca chelator. Under zero-trans conditions at a fixed (Na){sub i} = 10-160 mM with varying ({sup 45}Ca){sub 0} = 2.5 {minus}122 {mu}M for each (Na){sub i}, the K{sub m} and V{sub max} values increased from 7.7 to 33.5 {mu}M and from 2.3 to 9.0 nmol{center dot}mg{sup {minus}1}{center dot}s{sup {minus}1}, respectively. The V{sub max}/K{sub m} values show a {+-} 2-10% deviation from the average value of 0.274 nmol{center dot}mg{sup {minus}1}{center dot}s{sup {minus}1}{center dot}{mu}M{sup {minus}1} over the whole range of (Na){sub i}. This suggests that, under conditions in which V{sub max} and K{sub m} are (Na){sub i} dependent and vary 4-5-fold, the V{sub max}/K{sub m} values are constant within the experimental error. In the presence of K{sup +}-valinomycin the V{sub max}/K{sub m} values are 0.85 {+-} 0.17 and 1.08 {+-} 0.18 nmol{center dot}mg{sup {minus}1}{center dot}s{sup {minus}1}{center dot}{mu}M{sup {minus}1} at (Na){sub i} = 20 and 160 mM, respectively, suggesting that under conditions of short circuit of the membrane potential the V{sub max}/K{sub m} values still exhibit the (Na){sub i} independence. The presented data support a Ping-Pong (consecutive) mechanism of cation transport in the Na{sup +}-Ca{sup 2+} exchanger.

• OSTI ID: 6073988
• Journal Information: Biochemistry; (USA), Vol. 29:10; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CALCIUM 45
UPTAKE
CARBON 14 COMPOUNDS
MEMBRANE TRANSPORT
BIOCHEMICAL REACTION KINETICS
CATIONS
EDTA
HEART
LIPOSOMES
SODIUM COMPOUNDS
ALKALI METAL COMPOUNDS
ALKALINE EARTH ISOTOPES
AMINO ACIDS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BODY
CALCIUM ISOTOPES
CARBOXYLIC ACIDS
CARDIOVASCULAR SYSTEM
CELL CONSTITUENTS
CHARGED PARTICLES
CHELATING AGENTS
DAYS LIVING RADIOISOTOPES
EVEN-ODD NUCLEI
INTERMEDIATE MASS NUCLEI
IONS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANOIDS
ORGANS
RADIOISOTOPES
REACTION KINETICS
550201* - Biochemistry- Tracer Techniques