Attenuation of calmodulin regulation evokes Ca2+ oscillations: evidence for the involvement of intracellular arachidonate-activated channels and connexons

• Published in: Molecular and cellular biochemistry 2019-06, Vol.456 (1-2), p.191-204
• Main Authors: Turovsky, Egor A., Zinchenko, Valery P., Kaimachnikov, Nikolai P.
• Format: Article
• Language: English
• Subjects: Adipocytes; Attenuation; Biochemistry; Biomedical and Life Sciences; Calcium antagonists; Calcium channels; Calcium ions; Calcium mobilization; Calcium signalling; Calcium transport; Calcium-binding protein; Calmodulin; Cardiology; Channels; Inositol 1,4,5-trisphosphate receptors; Intracellular; Life Sciences; Medical Biochemistry; Octanol; Oncology; Organelles; Oscillations; Phospholipase; Phospholipase A2; Phospholipase C; Receptors; Ryanodine; Thapsigargin; Transport; Trifluoperazine
• ISSN: 0300-8177; 1573-4919
• DOI: 10.1007/s11010-019-03504-z

Intracellular Са 2+ controls its own level by regulation of Ca 2+ transport across the plasma and organellar membranes, often acting via calmodulin (CaM). Drugs antagonizing CaM action induce an increase in cytosolic Ca 2+ concentration in different cells. We have found persistent Са 2+ oscillations in cultured white adipocytes in response to calmidazolium (CMZ). They appeared at [CMZ] > 1 μM as repetitive sharp spikes mainly superimposed on a transient or elevated baseline. Similar oscillations were observed when we used trifluoperazine. Oscillations evoked by 5 μM CMZ resulted from the release of stored Ca 2+ and were supported by Са 2+ entry. Inhibition of store-operated channels by YM-58483 or 2-APB did not change the responses. Phospholipase A 2 inhibited by AACOCF 3 was responsible for initial Ca 2+ mobilization, but not for subsequent oscillations, whereas inhibition of iPLA 2 by BEL had no effect. Phospholipase C was partially involved in both stages as revealed with U73122. Intracellular Са 2+ stores engaged by CMZ were entirely dependent on thapsigargin. The oscillations existed in the presence of inhibitors of ryanodine or inositol 1,4,5-trisphosphate receptors, or antagonists of Ca 2+ transport by lysosome-like acidic stores. Carbenoxolone or octanol, blockers of hemichannels (connexons), when applied for two hours, prevented oscillations but did not affect the initial Са 2+ release. Incubation with La 3+ for 2 or 24 h inhibited all responses to CMZ, retaining the thapsigargin-induced Ca 2+ rise. These results suggest that Ca 2+ -CaM regulation suppresses La 3+ -sensitive channels in non-acidic organelles, of which arachidonate-activated channels initiate Ca 2+ oscillations, and connexons are intimately implicated in their generation mechanism.