Non-stimulated Ca2+ leak pathway in cerebellar granule neurones.
The aim of this study was to investigate the pathways of calcium influx routes in non-stimulated cerebellar granule neurones by use of standard microspectrofluorimetric techniques. Repetitive application of Ca2+-free solutions for various time intervals induced decreases of resting cytosolic free Ca2+ concentration ([Ca2+]i) which were followed, on Ca2+ readmission, by a full recovery, always to the initial resting [Ca2+]i levels. Use of drugs to deplete calcium stores (thapsigargin, alone or combined with low levels of ionomycin) did not cause release of Ca2+ from the intracellular stores nor enhanced the activity of the Ca2+ entry pathway. This influx was mainly independent of voltage operated calcium channels, since both L-type channel blockers (nitrendipine) and the hyperpolarizing agent pinacidil (a K+-channel opener) were without effect. Contribution from glutamate receptors to this influx was eliminated since a combination of blockers of NMDA and AMPA glutamate receptors (NBQX and D-AP5) did not affect the properties of the Ca2+ response. The Ca2+ leak pathway was sensitive to micromolar levels of lanthanum and gadolinium, and to the compound 2-APB, features shared by several channels of the TRP superfamily. In summary, our results show the presence of a Ca2+ permeable pathway, active and patent in resting conditions in cerebellar granule neurones, and which is different from the voltage-operated calcium channels and not operated by depletion of the stores.
Pinilla
P J Gómez
PJ
Department of Physiology, University of Extremadura, Fac Vet Sci and Nursing School, 10071 Cáceres, Spain.
Hernández
A T
AT
Camello
M C
MC
Pozo
M J
MJ
Toescu
E C
EC
Camello
P J
PJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured; D002531:Cerebellum / Q000378:metabolism*; D028581:Lanthanoid Series Elements / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D019284:Thapsigargin / Q000494:pharmacology
D015220:Calcium Channels; D028581:Lanthanoid Series Elements; D019284:Thapsigargin; D002118:Calcium