Dynamic and static calcium gradients inside large snail (Helix aspersa) neurones detected with calcium-sensitive microelectrodes.
We have used quartz Ca2+-sensitive microelectrodes (CASMs) in large voltage-clamped snail neurones to investigate the inward spread of Ca2+ after a brief depolarisation. Both steady state and [Ca2+]i transients changed with depth of penetration. When the CASM tip was within 20 microm of the far side of the cell the [Ca2+]i transient time to peak was 4.4+/-0.5s, rising to 14.7+/-0.7s at a distance of 80 microm. We estimate that the Ca2+ transients travelled centripetally at an average speed of 6 microm2 s(-1) and decreased in size by half over a distance of about 45 microm. Cyclopiazonic acid had little effect on the size and time to peak of Ca2+ transients but slowed their recovery significantly. This suggests that the endoplasmic reticulum curtails rather than reinforces the transients. Injecting the calcium buffer BAPTA made the Ca2+ transients more uniform in size and increased their times to peak and rates of recovery near the membrane. We have developed a computational model for the transients, which includes diffusion, uptake and Ca2+ extrusion. Good fits were obtained with a rather large apparent diffusion coefficient of about 90+/-20 microm2 s(-1). This may assist fast recovery by extrusion.
Thomas
Roger C
RC
Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK. rct26@cam.ac.uk
Postma
Marten
M
D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D015374:Biosensing Techniques / Q000379:methods*; D002021:Buffers; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology; D002245:Carbon Dioxide / Q000494:pharmacology; D002478:Cells, Cultured; D003198:Computer Simulation; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006372:Helix, Snails / Q000378:metabolism*; D008839:Microelectrodes; D009474:Neurons / Q000378:metabolism*; D011791:Quartz
D001639:Bicarbonates; D002021:Buffers; D002245:Carbon Dioxide; D011791:Quartz; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium