Depolarization-evoked Ca2+ release in a non-excitable cell, the rat megakaryocyte.
1. The effect of membrane potential on [Ca2+]i in rat megakaryocytes was studied using simultaneous whole-cell patch clamp and fura-2 fluorescence recordings. 2. Depolarization from -75 to 0 mV had no effect on [Ca2+]i in unstimulated cells, but evoked one or more spikes of Ca2+ increase (peak increase: 714 +/- 95 nM) during activation of metabotropic purinoceptors by 1 microM ADP. 3. The depolarization-evoked Ca2+ increase was present in Ca2+-free medium and also following removal of Na+. Thus depolarization mobilizes Ca2+ from an intracellular store without a requirement for altered Na+-Ca2+ exchange activity. 4. Intracellular dialysis with heparin blocked the depolarization-evoked Ca2+ increase, indicating a role for functional IP3 receptors. 5. Under current clamp, ADP caused the membrane potential to fluctuate between -43 +/- 1 and -76 +/- 1 mV. Under voltage clamp, depolarization from -75 to -45 mV evoked a transient [Ca2+]i increase (398 +/- 91 nM) during exposure to ADP. 6. We conclude that during stimulation of metabotropic purinoceptors, membrane depolarization over the physiological range can stimulate Ca2+ release from intracellular stores in the rat megakaryocyte, a non-excitable cell type. This may represent an important mechanism by which electrogenic influences can control patterns of [Ca2+]i increase.
Mahaut-Smith
M P
MP
Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK. mpm11@cam.ac.uk
Hussain
J F
JF
Mason
M J
MJ
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004594:Electrophysiology; D006493:Heparin / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008533:Megakaryocytes / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D011983:Receptors, Purinergic / Q000187:drug effects / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology
D011983:Receptors, Purinergic; D000244:Adenosine Diphosphate; D006493:Heparin; D012964:Sodium; D002118:Calcium