Spontaneous [Ca2+]i fluctuations in rat chromaffin cells do not require inositol 1,4,5-trisphosphate elevations but are generated by a caffeine- and ryanodine-sensitive intracellular Ca2+ store.

摘要: A considerable fraction (65%) of single rat chromaffin cells loaded with the fluorescent [Ca2+]i indicator fura-2 exhibited spontaneous rhythmic fluctuations an average period approximately 100 s. Parallel patch clamp experiments as well carried out in Ca2(+)-free and other modified media presence Ca2+ Na+ channel blockers indicated origin from intracellular stores. Appropriate concentrations agonists (bradykinin histamine) for receptors (B2 H1) that trigger generation inositol 1,4,5-trisphosphate induced increased fluctuation frequency, recruitment silent cells, large changes at high doses. These effects were blocked by cell pretreatment neomycin, a drug inhibits generation. In contrast, another drug, caffeine, which also frequency recruitment, unaffected neomycin. Ryanodine caused first prolongation then (approximately 10 min) block both caffeine effects, where transients after bradykinin histamine maintained. Caffeine ryanodine are known to affect selectively process calcium-induced release; this is demonstration activity arising Ca2(+)-induced release nonmuscle no strict requirement involvement.