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Mg2+ buffering in cultured chick ventricular myocytes: quantitation and modulation by Ca2+
K L Koss1, R W Putnam, R D Grubbs
1Department of Pharmacology and Toxicology, School of Medicine, Wright State University, Dayton, Ohio 45435.
The American Journal of Physiology
|May 1, 1993
Summary
Chick ventricular myocytes exhibit significant magnesium buffering, quantified by a new Mg2+ buffer coefficient (BMg). This buffering is influenced by cytosolic calcium levels, suggesting distinct calcium-sensitive and insensitive pools.
Area of Science:
- Cardiovascular Physiology
- Cellular Biophysics
- Ion Homeostasis
Background:
- Cytosolic magnesium (Mg2+) plays a crucial role in cellular function, but its buffering mechanisms are not fully understood.
- Adenosine triphosphate (ATP) chelates a significant portion of intracellular Mg2+.
- Understanding Mg2+ buffering is vital for comprehending cellular energy metabolism and signaling.
Purpose of the Study:
- To characterize the Mg2+ buffering capacity of cultured chick ventricular myocytes.
- To quantify Mg2+ buffering using a novel Mg2+ buffer coefficient (BMg).
- To investigate the influence of extracellular calcium (Ca2+) on Mg2+ buffering.
Main Methods:
- Cultured chick ventricular myocytes were utilized to study Mg2+ buffering.
- ATP was depleted to liberate Mg2+ normally chelated by ATP.
- Cytosolic Mg2+ and Ca2+ activity were measured using mag-fura-2 fluorescence.
- Experiments were conducted with and without extracellular Ca2+.
Main Results:
- A significant Mg2+ buffering capacity was identified, with a calculated Mg2+ buffer coefficient (BMg) of 1.4 when extracellular Ca2+ is present.
- In the absence of extracellular Ca2+, Mg2+ buffering increased (BMg = 2.5), and basal cytosolic Ca2+ activity decreased by 72%.
- The data indicate that cytosolic Ca2+ activity influences Mg2+ buffering, suggesting the presence of both Ca2+-sensitive and Ca2+-insensitive Mg2+ pools.
Conclusions:
- Chick ventricular myocytes possess substantial Mg2+ buffering capacity.
- Mg2+ buffering is composed of at least two components: a Ca2+-insensitive adenine nucleotide pool and a Ca2+-sensitive non-adenine nucleotide pool.
- Extracellular Ca2+ plays a role in modulating cytosolic Mg2+ activity and buffering in these cells.