Ca2+ signalling in rat chromaffin cells: interplay between Ca2+ release from intracellular stores and membrane potential.
Cytosolic Ca2+ oscillations are physiologically important in a range of excitable and non-excitable cells. The combined techniques of whole-cell patch clamp and photometric measurement of cytosolic Ca2+ has enabled us to identify the components of Ca2+ spiking in rat chromaffin cells. We show that Ca2+ oscillations continue at a fixed membrane potential and that infusion of the InsP3 receptor antagonist, heparin, substantially blocked the cytosolic Ca2+ spikes. However, even in the presence of heparin we observed spikes of membrane potential depolarization due to the repetitive activation of a transient inward cation current. We conclude that Ca2+ oscillations are dependent on Ca2+ release from heparin sensitive Ca2+ stores and possibly on Ca2+ entry associated with the repetitive activation of a transient cation current. The depolarizing action of the cation current would, in turn, recruit voltage-sensitive Ca2+ channels and further Ca2+ entry would augment the cytosolic Ca2+ spikes. Our results demonstrate that Ca2+ oscillations in rat chromaffin cells are due to a complex interplay of Ca2+ entry and Ca2+ release.
D'Andrea
P
P
Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, Trieste, Italy.
Thorn
P
P
D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002412:Cations; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
D002412:Cations; D015544:Inositol 1,4,5-Trisphosphate; D001920:Bradykinin; D002118:Calcium