MLCK reciprocally regulates capacitative calcium entry and non-capacitative calcium entry in intracellular calcium influx process in mouse parotid gland acinar cells

Abstract

Arachidonic acid (AA) regulates intracellular calcium concentration in a variety of cell types. In the present study, the effects of serine/threonine phosphatases and myosin light chain kinase (MLCK) on AA-induced Ca²⁺ signaling in mouse parotid acinar cells were investigated.

Treatment of acinar cells with MLCK inhibitors, ML9 and wortmannin, thapsigargin-induced Ca²⁺ entry (capacitative Ca²⁺ entry: CCE) was partially blocked. In contrast, AA-induced Ca²⁺ entry (noncapacitative Ca²⁺ entry: NCCE) was attenuated by wortmannin but increased by ML9. Calyculin A, a protein phosphatase (PP) inhibitor, resulted in an enhancement of AA-induced Ca²⁺ entry. Our previous study suggested that this inhibition of PP resulted in an enhancement of AA-induced Ca²⁺ entry via PKA. In the presence of ML9, AA-induced Ca²⁺ influx enhanced by calyculin A was further increased. However, even when the order of ML9 administration was changed, the enhancement of AA-induced Ca²⁺ entry by calyculin A was not changed. Taking everything into consideration, MLCK partially enhances CCE, but suppresses AA-induced Ca²⁺ entry, i.e. NCCE. MLCK is probably present in the vicinity of PKA and is presumed to have a cooerative effect on the PKA response against CCE and NCCE.