Neurotensin induces calcium oscillations in cultured amacrine cells

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Abstract
The peptide, neurotensin, is found in a class of amacrine cells synapsing chiefly withother amacrine cells in the chicken retina (Li & Lam, 1990; Watt et al., 1991). Toinvestigate the possible effects of neurotensin, we have used Ca2+imaging to measure cytosolic Ca2+concentrations in cultured chick amacrine cells. Following a delay of about 2 min, neurotensin (300 nM) induced oscillations in Ca2+concentration that typically had a period of 2 min and peak values of about 300 nM when averaged over the cell body. The phospholipase C inhibitors U-73, 112 and 4′-bromophenacyl bromide terminated oscillations induced by neurotensin but the protein kinase inhibitors H7 and staurosporine did not inhibit oscillations, increasing their frequency instead. In the absence of external Ca2+, neurotensin induced only a single Ca2+transient, much briefer than when external Ca2+was present. Together these results suggest that neurotensin activates phospholipase C, thereby producing IP3that triggers Ca2+release from an internal store. Although this released Ca2+contributes to periodic Ca2+peaks, the majority of cytosolic Ca2+, even in the first peak, comes from Ca2+influx across the plasmalemma.