Temporal relationships between Ca2+ store mobilization and Ca2+ entry in an exocrine cell

Area of Science:

• Cellular Biology
• Physiology
• Biochemistry

Background:

• Agonist-induced calcium (Ca2+) entry is crucial in non-excitable cells.
• Current models predict distinct temporal relationships between Ca2+ release and entry.

Purpose of the Study:

• To investigate the temporal dynamics of Ca2+ entry activation following agonist stimulation.
• To differentiate between existing models of Ca2+ entry in avian exocrine cells.

Main Methods:

• Measurements of intracellular Ca2+ ([Ca2+]i) and Mn2+ quench in individual avian exocrine cells.
• Stimulation with inositol trisphosphate (Ins(1,4,5)P3) and thapsigargin.
• Inhibition studies using SK&F 96365 and assessment of inositol tetrakisphosphate (Ins(1,3,4,5)P4) generation.

Main Results:

• Ins(1,4,5)P3-induced Ca2+ release occurred within 3-5 seconds.
• Mn2+ quench, reflecting Ca2+ entry, was delayed by 20-30 seconds.
• The delay was not caused by elevated [Ca2+]i or Ins(1,3,4,5)P4 generation.

Conclusions:

• The observed delay supports capacitative models of Ca2+ entry.
• Ca2+ entry activation requires a messenger generated by intracellular Ca2+ store depletion.
• This messenger is transmitted to the plasma membrane to activate entry pathways.