CA2-ACTIVATED K+ CHANNELS ARE INVOLVED IN REGULATORY VOLUME DECREASE IN ACINAR-CELLS ISOLATED FROM THE RAT LACRIMAL GLAND()

The volumes of acinar cells isolated from rat lacrimal gland were meas ured on computer by videoimaging. Cells were found to swell on exposur e to hypotonic solutions; they subsequently exhibited a regulatory vol ume decrease (RVD). RVD was inhibited in the absence of extracellular Ca2+, and by the K+ channel blocker tetraethylammonium chloride (2 mM TEA(+)). The possible involvement of K+ channels in RVD was further in vestigated in cell-attached patches. Exposing the cells to a hypotonic solution activated channels with a conductance of 141 +/- 6 pS (n = 1 1). These channels were partially blocked by 0.5 mM TEA(+), and channe l activation was not observed in the absence of extracellular Ca2+. Ex periments in the inside-out patch configuration demonstrated that the channels activated by hypotonic stress were ''maxi'' Ca2+-activated K channels. It is concluded that the opening of these channels plays an important role in RVD, by facilitating K+ loss from the cell.