Distinct Mechanisms of [Ca2+]i Oscillations in HSY and HSG Cells: Role of Ca2+ Influx and Internal Ca2+ Store Recycling

This study examined Ca²⁺]_i oscillations in the human salivary gland cell lines, HSY and HSG. Relatively low concentrations of carbachol (CCh) induced oscillatory, and higher CCh] induced sustained, steady-state increases in Ca²⁺]_i and K _Ca currents in both cell types. Low IP₃, but not thapsigargin (Tg), induced Ca²⁺]_i oscillations, whereas Tg blocked CCh-stimulated Ca²⁺]_i oscillations in both cell types. Unlike in HSG cells, removal of extracellular Ca²⁺ from HSY cells (i) did not affect CCh-stimulated Ca²⁺]_i oscillations or internal Ca²⁺ store refill, and (ii) converted high CCh]-induced steady-state increase in Ca²⁺]_i into oscillations. CCh- or thapsigargin-induced Ca²⁺ influx was higher in HSY, than in HSG, cells. Importantly, HSY cells displayed relatively higher levels of sarcoendoplasmic reticulum Ca²⁺ pump (SERCA) and inositoltrisphosphate receptors (IP₃Rs) than HSG cells. These data demonstrate that Ca²⁺]_i oscillations in both HSY and HSG cells are primarily determined by the uptake of Ca²⁺ from, and release of Ca²⁺ into, the cytosol by the SERCA and IP₃R activities, respectively. In HSY cells, Ca²⁺ influx does not acutely contribute to this process, although it determines the steady-state increase in Ca²⁺]_i. In HSG cells, Ca²⁺]_i oscillations directly depend on Ca²⁺ influx; Ca²⁺ coming into the cell is rapidly taken up into the store and then released into the cytosol. We suggest that the differences in the mechanism of Ca²⁺]_i oscillations HSY and HSG cells is related to their respective abilities to recycle internal Ca²⁺ stores. Received: 30 October 2000/Revised: 26 February 2001