The effect of mini-glucagon, the metabolite (19-29) of glucagon was examined on the sarcolemmal (SL) Ca2+ pump activity measured in situ, in single quiescent embryonic chick heart ventricular cells loaded with Fura-2. The method consisted in triggering limited cytosolic Ca2+ concentration ([Ca2+]i) pulses by the addition of the Ca2+ ionophore 4-bromo-A23187. [Ca2+]i decays, imposed by the addition of EGTA, were monitored in conditions in which only the SL Ca2+ pump could ensure [Ca2+]i removal, i.e. in the presence of the sarcoplasmic reticular (SR) Ca2+ pump specific inhibitor, thapsigargin, substituting NaCI by LiCI in the external medium in order to quench the Na+/Ca2+ exchanger, and under null Ca2+ gradient. Mini-glucagon elicited a dose-dependent inhibition of the SL Ca2+ pump, maximal 80% inhibition being observed with 1 nM mini-glucagon. In addition to its effect on the SL Ca2+ pump, mini-glucagon evoked a delayed onset of a [Ca2+]i oscillatory response in cells incubated in normal conditions. Both effects of mini-glucagon were mimicked by vanadate tested at 2 microM, a concentration at which it acts as a specific inhibitor of the SL Ca2+ pump. These results define the contribution of the cardiac sarcolemmal Ca2+ pump to Ca2+ homeostasis in situ and its role as a target for mini-glucagon action.