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Calcium transport in basolateral plasma membranes from kidney cortex of Milan hypertensive rats
Abstract:
Ca2+ transport was investigated in basolateral plasma membranes (BLM) isolated from kidney cortex of the Milan strain of genetically hypertensive rats (MHS) and their normotensive controls (MNS) during a pre-hypertensive stage (age 3-4 weeks). It was found that the Vmax of ATP-dependent Ca2+ transport (in the presence of calmodulin) was about 16% lower in MHS than in control rats. In membranes from MNS rats which had been isolated in the presence of EGTA, the ATP-dependent Ca2+ transport showed a hyperbolic Ca2+ concentration dependence, a high Km (Ca2+) and a low Vmax; upon addition of exogenous calmodulin, the kinetics became sigmoidal, the Km (Ca2+) was decreased and the Vmax was increased. In membranes from MHS rats, the Ca2+ concentration dependence of ATP-driven Ca2+ transport was sigmoidal and the Ca2+ affinity was high in the absence of added calmodulin. Addition of exogenous calmodulin to these membranes resulted in an increase in Vmax, but no change in other kinetic parameters. Low-affinity hyperbolic kinetics of Ca2+ transport could only be obtained in MHS rats if the membranes were extracted with hypotonic EDTA and hypertonic KCl. These data suggest that the plasma membrane Ca2+-ATPase, which catalyses the ATP-dependent Ca2+ transport, exists in BLM of pre-hypertensive MHS rats predominantly in an activated, high-affinity form.
Insights
Calcium (Ca2+) transport in kidney basolateral membranes (BLM) of pre-hypertensive rats shows altered kinetics in genetically hypertensive strains. This suggests the Ca2+-ATPase is predominantly in an activated, high-affinity state, impacting blood pressure regulation.
Area of Science:
- Biochemistry
- Physiology
- Nephrology
Background:
- Genetic hypertension involves altered ion transport in kidney basolateral membranes (BLM).
- Calcium (Ca2+) homeostasis is critical for regulating blood pressure and kidney function.
Purpose of the Study:
- To investigate Ca2+ transport kinetics in BLM of pre-hypertensive Milan hypertensive rats (MHS) compared to normotensive controls (MNS).
- To determine the role of calmodulin in modulating Ca2+ transport in MHS and MNS rats.
Main Methods:
- Isolation of basolateral plasma membranes (BLM) from kidney cortex of pre-hypertensive MHS and MNS rats.
- Assay of ATP-dependent Ca2+ transport kinetics (Vmax, Km) in the presence and absence of exogenous calmodulin.
- Membrane extraction techniques to assess Ca2+-ATPase activation states.
Main Results:
- ATP-dependent Ca2+ transport Vmax was approximately 16% lower in MHS rats compared to MNS rats.
- MNS rat BLM showed hyperbolic kinetics, high Km, and low Vmax, shifting to sigmoidal kinetics with increased affinity and Vmax upon calmodulin addition.
- MHS rat BLM exhibited sigmoidal kinetics and high Ca2+ affinity even without added calmodulin, with calmodulin increasing Vmax but not affinity.
Conclusions:
- The plasma membrane Ca2+-ATPase in BLM of pre-hypertensive MHS rats exists predominantly in an activated, high-affinity form.
- Altered Ca2+ transport kinetics may contribute to the development of hypertension in the MHS rat model.
- Calmodulin modulation of Ca2+-ATPase activity is altered in the pre-hypertensive state of genetic hypertension.