Changes in platelet free Ca2+ concentration after chronic digoxin treatment.

Area of Science:

• Cellular Physiology
• Cardiovascular Pharmacology

Background:

• Cellular sodium (Na+) and calcium (Ca2+) concentrations are interdependent, regulated by systems like Na+/Ca2+-exchanger and Na+/H+-exchanger.
• Excitable cells rely on Na+/Ca2+-transport for calcium homeostasis, influencing cellular functions.
• Understanding these dynamics is crucial for cellular signaling and drug effects.

Purpose of the Study:

• To investigate the impact of reduced membrane sodium gradient on cytosolic free calcium concentration ([Ca2+]i).
• To analyze changes in [Ca2+]i in human platelets and erythrocytes during digoxin treatment.

Main Methods:

• Measurement of cytosolic free Ca2+ concentration ([Ca2+]i) using fluorescent dyes.
• Analysis performed on platelets and erythrocytes from healthy subjects.
• Comparison of [Ca2+]i levels before and during a 6-day digoxin treatment regimen (0.25 mg/day).

Main Results:

• A significant increase in platelet [Ca2+]i was observed, rising from 169 ± 30 to 321 ± 61 nmol/l (P < 0.02).
• Erythrocyte [Ca2+]i remained unchanged (121 ± 6 vs 104 ± 7 nmol/l).
• The increase in platelet [Ca2+]i was not linked to serotonin content changes or acute ouabain exposure, suggesting indirect mechanisms.

Conclusions:

• The observed increase in platelet intracellular calcium during digoxin treatment is not a direct, short-term result of a reduced sodium gradient.
• Potential explanations include overload of intracellular calcium stores or enhanced in vivo stimulation by endogenous factors.
• Further research is needed to elucidate the precise mechanisms behind digoxin's effect on platelet calcium homeostasis.