LITHIUM-INDUCED DECREASE IN SPONTANEOUS CA2+ OSCILLATIONS IN SINGLE GH(3) RAT PITUITARY-CELLS

1 Measurement of [Ca2+](i) in single rat pituitary GH(3) cells by dynamic single cell imaging techniques demonstrated that under basal conditions there is a large variation in the temporal pattern of [Ca2+](i) signalling between individual cells ranging from high frequency asynchronous oscillations to quiescence. 2 We have reported previously that treatment of GH(3) cells with 1 mM Li+ (a concentration used therapeutically in the treatment of manic depression) for 7 days reduces basal and thyrotrophin-releasing hormone (TRH)-stimulated levels of mass inositol 1,4,5-trisphosphate [Ins(1,4,5)P-3]. In the present study, we show that this is associated with a reduction in the number of cells exhibiting basal Ca2+ oscillations over a sampling period of 60 s, whereas the maximum amplitude of oscillations is unaffected. 3 The pattern of [Ca2+](i) responses to the agonist TRH varied considerably between individual cells, making quantitation of the responses difficult; however, data obtained from measurements made on a population of cells showed that increases in peak [Ca2+](i) induced by high concentrations of TRH were reduced in cells treated with 1 mM Li+ for 7 days relative to control cells. 4 The sensitivity of the phosphoinositide pathway to [Ca2+](i) was investigated by loading GH(3) cells with BAPTA/AM at a concentration sufficient to lower 'basal' [Ca2+](i) in a population of cells and to inhibit agonist-stimulated increases in [Ca2+](i). Under these conditions, basal and TRH-stimulated mass Ins(1,4,5)P-3 levels were unaffected. 5 These results demonstrate that a 7-day Li+ treatment leads to an alteration in Ca2+ signalling, in particular by reducing the number of cells exhibiting high frequency Ca2+ oscillations under basal conditions. The significance of these results to the clinical effectiveness of Li+ in the treatment of manic depression is discussed.