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

Journal Article · Tue Mar 13 04:00:00 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), Journal Name: Biochemistry; (USA) Vol. 29:10; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

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