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 Ca(2+) concentration ([Ca(2+)](i)) in rat submandibular acinar cells during stimulation with acetylcholine (ACh, 1 micro M). These [Ca(2+)](i) oscillations were also induced by 1 micro M thapsigargin and were inhibited by 50 micro M La(3+), 1 micro M 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.