Depolarisation-evoked Ca2+ waves in the non-excitable rat megakaryocyte

1. A combination of patch clamp, confocal microscopy and immunohistochemist ry was used to examine the spatial properties of Ca2+ signalling in the rat megakaryocyte, a non-excitable cell type in which membrane potential can m arkedly modulate agonist-evoked Ca2+ release. C, 2. Intracellular calcium ion concentration ([Ca2+](i)) increases, stimulate d by both ADP and depolarisation, frequently originated from a peripheral l ocus and spread as a wave throughout the cell. Spatially restricted [Ca2+]( i) increases, consistent with elementary Ca2+ release events, were occasion ally observed prior to ADP-evoked waves. 3. ADP- and depolarisation-evoked Ca2+ waves travelled approximately twice as fast around the periphery of the cell compared to across its radius, lea ding to a curvilinear wavefront. There was no significant difference betwee n wave velocities generated by the two stimuli. 4. Immunohistochemical staining of type III IP3 receptors, the endoplasmic reticulum-specific protein GRP78/BiP and calreticulin indicated a major per ipheral location of the cellular Ca2+ stores which probably accounts for th e accelerated wave velocity at the cell periphery. 5. These data demonstrate that [Ca2+](i) increases, stimulated by depolaris ation or the agonist ADP, have indistinguishable spatial properties, provid ing evidence that similar underlying mechanisms are responsible for their g eneration.