[Ca 2+ ] i Oscillations Induced by High [K + ] o in Acetylcholine‐Stimulated Rat Submandibular Acinar Cells: Regulation by Depolarization, cAMP and Pertussis Toxin

Maintaining the extracellular K + concentration ([K + ] o ) between 15 and 60 mM induced oscillations in the intracellular Ca 2+ concentration ([Ca 2+ ] i ) in rat submandibular acinar cells during stimulation with acetylcholine (ACh, 1 μM). These [Ca 2+ ] i oscillations were also induced by 1 μM thapsigargin and were inhibited by 50 μM La 3+ , 1 μM Gd 3+ , or the removal of extracellular Ca 2+ , indicating that the [Ca 2+ ] i oscillations were generated by store‐operated Ca 2+ entry (SOC). The frequency of the ACh‐evoked [Ca 2+ ] 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 [Ca 2+ ] i oscillations at [K + ] o of 4.5 or 7.5 mM in ACh‐stimulated cells. These data suggest that depolarization causes [Ca 2+ ] i to oscillate in ACh‐stimulated submandibular acinar cells. Pertussis toxin (PTX, an inhibitor of G proteins) caused [Ca 2+ ] i to be sustained at a high level in ACh‐stimulated cells at 25 mM or 60 mM [K + ] o . This suggests that the [Ca 2+ ] 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 [Ca 2+ ] 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 ([Ca 2+ ] 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.