Related Experiment Videos
Active Ca2+ transport systems in basolateral membranes from rabbit distal colon
H Wiener1, M D de Jong, C H van Os
1Department of Physiology, University of Nijmegen, The Netherlands.
Journal of Internal Medicine. Supplement
|January 1, 1990
Summary
Rabbit distal colon epithelial cells regulate sodium influx via a feedback mechanism. This study found that (Ca2+, Mg2+)-ATPase, not Na+/Ca2+ exchange, is the primary system for calcium extrusion in these cells.
Area of Science:
- Physiology
- Cell Biology
- Epithelial Transport
Background:
- Active sodium (Na+) absorption in epithelia like the distal colon involves feedback inhibition of Na+ influx.
- Increasing intracellular Na+ concentration ([Na+]) is thought to elevate intracellular Ca2+ concentration ([Ca2+]) via basolateral Na+/Ca2+ exchange.
Purpose of the Study:
- To characterize Ca2+ transporting systems in rabbit distal colon basolateral membranes.
- To investigate the role of Na+/Ca2+ exchange in regulating intracellular Ca2+ in this tissue.
Main Methods:
- Isolation of basolateral membrane vesicles from rabbit distal colon surface cells.
- Measurement of ATP-dependent Ca2+ uptake kinetics.
- Assessment of Na+ gradient-driven Ca2+ transport.
Main Results:
- Demonstrated ATP-dependent Ca2+ uptake with specific kinetic parameters (Km = 0.09 µM, Vm = 3.8 nmol/mg/min).
- ATP-dependent Ca2+ transport was insensitive to ruthenium red and oxalate, indicating a plasma membrane origin.
- Absence of significant Ca2+ release upon Na+ addition and no Na+ gradient-stimulated Ca2+ uptake, refuting Na+/Ca2+ exchange activity.
Conclusions:
- The rabbit distal colon epithelium primarily utilizes (Ca2+, Mg2+)-ATPase as the sole Ca2+ extrusion system.
- A well-defined Na+/Ca2+ exchange system is absent in this tissue.
- Alternative mechanisms for coupling intracellular Na+ and Ca2+ concentrations are proposed.