Depolarisation-evoked Ca2+ waves in the non-excitable rat megakaryocyte.
1. A combination of patch clamp, confocal microscopy and immunohistochemistry was used to examine the spatial properties of Ca2+ signalling in the rat megakaryocyte, a non-excitable cell type in which membrane potential can markedly modulate agonist-evoked Ca2+ release. 2. Intracellular calcium ion concentration ([Ca2+]i) increases, stimulated by both ADP and depolarisation, frequently originated from a peripheral locus and spread as a wave throughout the cell. Spatially restricted [Ca2+]i increases, consistent with elementary Ca2+ release events, were occasionally 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, leading to a curvilinear wavefront. There was no significant difference between 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 peripheral location of the cellular Ca2+ stores which probably accounts for the accelerated wave velocity at the cell periphery. 5. These data demonstrate that [Ca2+]i increases, stimulated by depolarisation or the agonist ADP, have indistinguishable spatial properties, providing evidence that similar underlying mechanisms are responsible for their generation.
Thomas
D
D
Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK.
Mason
M J
MJ
Mahaut-Smith
M P
MP
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002467:Cell Nucleus / Q000502:physiology; D016764:Cell Polarity / Q000502:physiology; D004594:Electrophysiology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D007150:Immunohistochemistry; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008533:Megakaryocytes / Q000378:metabolism*; D018613:Microscopy, Confocal; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar
D000244:Adenosine Diphosphate; D002118:Calcium