Plasma membrane Ca2+ pumps and Na+/Ca2+ exchangers.

Area of Science:

• Cellular Biology
• Biochemistry
• Physiology

Background:

• Intracellular Ca2+ homeostasis is crucial and maintained by membrane transport systems.
• ATP-driven Ca2+ pumps and Na+/Ca2+ exchangers are key for Ca2+ extrusion across the plasma membrane.
• Ca2+ pumps are ubiquitous, possess high Ca2+ affinity, and are calmodulin-regulated; Na+/Ca2+ exchangers are vital in excitable tissues for bulk Ca2+ efflux.

Purpose of the Study:

• To review the molecular characterization and functional properties of Ca2+ transporting systems.
• To highlight advances in understanding Ca2+ pump isoforms and Na+/Ca2+ exchanger kinetics and regulation.
• To emphasize the potential for improved knowledge of ion transporter function.

Main Methods:

• Molecular characterization of Ca2+ pumps, including amino acid sequencing and domain identification.
• Genetic analysis of Ca2+ pump diversity through multigene families and alternative RNA splicing.
• Kinetic, stoichiometric, and regulatory studies of Na+/Ca2+ exchangers, aided by expression cloning.

Main Results:

• Complete amino acid sequences and functional domains of several Ca2+ pump isoforms have been identified.
• Mammalian Ca2+ pump diversity arises from multigene families and alternative splicing, leading to varied regulatory properties.
• Detailed kinetic and regulatory properties of Na+/Ca2+ exchangers have been established, promising molecular-level insights.

Conclusions:

• Advances in molecular characterization are enhancing our understanding of Ca2+ pumps and Na+/Ca2+ exchangers.
• Isoform diversity in Ca2+ pumps suggests tissue-specific physiological roles.
• Ongoing research on Na+/Ca2+ exchangers is rapidly improving knowledge of their molecular functions.