The role of Ca2+ feedback in shaping InsP3-evoked Ca2+ signals in mouse pancreatic acinar cells.
1. Cytosolic Ca2+ has been proposed to act as both a positive and a negative feedback signal on the inositol trisphosphate (InsP3) receptor. However, it is unclear how this might affect the Ca2+ response in vivo. 2. Mouse pancreatic acinar cells were whole-cell patch clamped to record the Ca2+-dependent chloride (Cl(Ca)) current spikes and imaged to record the cytosolic Ca2+ spikes elicited by the injection of Ins(2,4,5)P3. Increasing concentrations of Ca2+ buffer (up to 200 microM EGTA or BAPTA) were associated with the appearance of steps in the current activation phase and a prevalence of smaller-amplitude Cl(Ca) spikes. Imaging experiments showed that with increased buffer the secretory pole cytosolic Ca2+ signal became fragmented and spatially discrete Ca2+ release events were observed. 3. At higher buffer concentrations (200-500 microM), increasing concentrations of EGTA increased spike frequency and reduced spike amplitude. In contrast, BAPTA decreased spike frequency and maintained large spike amplitudes. 4. We conclude that, during InsP3-evoked spiking, long-range Ca2+ feedback ( approximately 2-4 microm) shapes the rising phase of the Ca2+ signal by acting to co-ordinate discrete Ca2+ release events and short-range ( approximately 40 nm) Ca2+ feedback acts to inhibit further Ca2+ release.
Kidd
J F
JF
The Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, UK.
Fogarty
K E
KE
Tuft
R A
RA
Thorn
P
P
D000085:Acetates / Q000494:pharmacology; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D005029:Ethylenediamines / Q000494:pharmacology; D005246:Feedback / Q000502:physiology; D005456:Fluorescent Dyes; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D010179:Pancreas / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010782:Photolysis
D000085:Acetates; D002021:Buffers; D002614:Chelating Agents; D005029:Ethylenediamines; D005456:Fluorescent Dyes; C057014:DM-nitrophen; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium