[Ca²⁺]_i Oscillations Induced by High [K⁺]_o in Acetylcholine‐Stimulated Rat Submandibular Acinar Cells: Regulation by Depolarization, cAMP and Pertussis Toxin

Abstract

Maintaining the extracellular K+ concentration ([K+]o) between 15 and 60 mM induced oscillations in the intracellular Ca2+ concentration ([Ca2+]i) in rat submandibular acinar cells during stimulation with acetylcholine (ACh, 1 μM). These [Ca2+]i oscillations were also induced by 1 μM thapsigargin and were inhibited by 50 μM La3+, 1 μM Gd3+, or the removal of extracellular Ca2+, indicating that the [Ca2+]i oscillations were generated by store‐operated Ca2+ entry (SOC). The frequency of the ACh‐evoked [Ca2+]i oscillations increased from 0.8 to 2.3 mHz as [K+]o was increased from 15 to 50 mM. TEA (an inhibitor of K+ channels) also induced [Ca2+]i oscillations at [K+]o of 4.5 or 7.5 mM in ACh‐stimulated cells. These data suggest that depolarization causes [Ca2+]i to oscillate in ACh‐stimulated submandibular acinar cells. Pertussis toxin (PTX, an inhibitor of G proteins) caused [Ca2+]i to be sustained at a high level in ACh‐stimulated cells at 25 mM or 60 mM [K+]o. This suggests that the [Ca2+]i oscillations are generated by a periodic inactivation of the SOC channels via PTX‐sensitive G proteins, which are stimulated by depolarization. Moreover, in the presence of DBcAMP or forskolin which accumulated cAMP the frequency of the [Ca2+]i oscillations remained constant (approximately 1.2 mHz) when [K+]o was maintained in the range 25‐60 mM. Based on these observations in ACh‐stimulated submandibular acinar cells, we conclude that depolarization stimulates the PTX‐sensitive G proteins, which inactivate the SOC channels periodically ([Ca2+]i oscillation), while hyperpolarization or PTX inhibits the G proteins, maintaining the activation of the SOC channels. Accumulation of cAMP is likely to modulate the PTX‐sensitive G proteins.

Implantable Three-Dimensional Salivary Spheroid Assemblies Demonstrate Fluid and Protein Secretory Responses to Neurotransmitters

“…3 Several reports showed increases in Ca i upon treatment with acetylcholine (or carbachol) in parotid or submandibular acini and dissociated cells. [46][47][48][49][50][51] Here we demonstrated the induction of calcium oscillations upon neurotransmitter stimulation of 3D acini-like spheroids in a human-compatible hydrogel culture system. The increase in Ca i and the recurring oscillations induced by acetylcholine among our 2.5D and 3D cultures indicates a functional fluid production pathway.…”

HCO3 −-dependent transient acidification induced by ionomycin in rat submandibular acinar cells

“…from the intracellular stores. In salivary cells [7][8][9][10][11][12][13][14][15], IM is used to activate SOCs, similarly to thapsigargin (TG) and acetylcholine (ACh).…”

Cytosolic calcium oscillations in submandibular gland cells1

“…The fact that large amounts of potassium ion are secreted after stimulation of the salivary glands has long been noted, but the physiological significance of the secreted potassium has never been properly addressed [20,[25][26][27] .…”

“…To trace the possible source of this unique property, we looked for typical differences in salivary acinar cells and other exocrine acinar cells and found significant differences in the extracellular fluid that bathe the cells and the gradual changes in saliva composition. Yoshida et al [26] made the initial discovery that when the potassium concentration in Kreb's buffer was raised (to 30 mmol/L), ACh-induced calcium increases changed dramatically from plateau increases to oscillatory increases. This discovery was confirmed in our laboratory (Figure 3).…”