The caffeine‐sensitive Ca²⁺ store in bovine adrenal chromaffin cells; an examination of its role in triggering secretion and Ca²⁺ homeostasis

Abstract

The effect of caffeine on catecholamine secretion and intracellular free Ca 2+ concentration ([Ca2+]i) in bovine adrenal chromaffin cells was examined using single fura-2-1oaded cells and cell populations. In cell populations caffeine elicited a large (~ 200 nM) transient rise in [Ca2+]i that was independent of external Ca 2+ . This rise in [CaZ+]i triggered little secretion. Single cell measurements of [Ca2+]i showed that most cells responded with a large (> 200 nM) rise in [Ca2+]~, whereas a minority failed to respond. The latter, whose caffeine-sensitive store was empty, buffered a Ca z+ load induced by a depolarizing stimulus more effectively than those whose store was full. The caffeine-sensitive store in bovine chromaffin cells may be involved in Ca 2+ homeostasis rather than in triggering exocytosis.

Activation of exocytosis by GTP analogues in adrenal chromaffin cells revealed by patch‐clamp capacitance measurement

“…In addition, external perfusion of the cells with caffeine which produces a marked mobilisation of intracellular Ca*' [21] The pipette buffer contained no addition, 10 mM XTP, 100 ,uM GppNHp or 1 mM GDP/B and capacitance followed over the initial 7 min period following establishment of whole-cell recording. exocytosis is complicated by cellular heterogeneity and the fact that the measurements are dependent upon release of catecholamine from the granule core as well as exocytotic membrane fusion.…”

Vesicular Ca2+ Participates in the Catalysis of Exocytosis

“…The most well characterized mechanism for exocytosis is elevation of [Ca 2ϩ ] i arising from influx of Ca 2ϩ though voltagegated or ligand-operated Ca 2ϩ channels (38). However, when this source of Ca 2ϩ is no longer available, Ca 2ϩ from intracellular stores can evoke exocytosis (19,39). The mobilization of intracellular Ca 2ϩ in bovine chromaffin cells also can lead to the opening of Ca 2ϩ channels in the plasma membrane to admit Ca 2ϩ from the exterior (40).…”

Excitatory amino acid regulation of intracellular Ca2+ in isolated catfish cone horizontal cells measured under voltage- and concentration- clamp conditions

“…These stores have been previously described in muscle (Fill and Coronado, 1988), sensory and sympathetic neurons (Lipscombe et al, 1988;Thayer et al, 1988a,b) and sea urchin eggs (Norden et al, 199 1) and appear to be functionally (Thayer et al, 1988b;Cheek et al, 1990;Malgaroli et al, 1990), pharmacologically (Palade et al, 1989), and anatomically (Burgoyne et al, 1989) distinct from IP,-sensitive stores. Intracellular Ca*+ can also increase following influx through voltage-dependent Ca*+ channels in those cells that express these channels.…”