Role of intracellular calcium in fast and slow desensitization of P2-receptors in PC12 cells.
1. Combined whole-cell patch clamp recording and confocal laser scanning microscopy of [Ca2+]i transients were performed on single PC12 cells to study any correlation between membrane currents induced by ATP and elevation in [Ca2+]i. ATP was applied by pressure from micropipettes near the recorded PC12 cells continuously superfused at a fast rate. 2. Brief (20 ms) pulses of ATP elicited monophasic inward currents and [Ca2+]i increases. Long applications (2 s) of ATP (5 mM) evoked peak currents which rapidly faded during the pulse and were followed by a large rebound current, interpreted as due to rapid desensitization and recovery of P2-receptors. The associated [Ca2+]i increase grew monotonically to a peak reached only after the occurrence of the current rebound, indicating that it is unlikely this cation has a role in fast desensitization. 3. Both membrane currents and [Ca2+]i transients were linearly dependent on holding membrane potential, suggesting that Ca2+ influx is the predominant cause of [Ca2+]i elevation. This view was supported by experiments carried out in Ca(2+)-free solution. 4. Brief pulses of ATP applied after a desensitizing pulse (2 s) of the same elicited smaller inward currents and [Ca2+]i rises indicating a role for [Ca2+]i in controlling slow desensitization of P2-receptors. 5. This notion was confirmed in experiments with various [Ca2+]i chelators which differentially affected slow desensitization in relation to their buffering capacity, while sparing fast receptor desensitization. 6. These results suggest a role for [Ca2+]i in slow rather than fast desensitization of P2-receptors, thus proposing this divalent cation as an intracellular factor able to provide an efficient and reversible control over receptor activity induced by ATP.
Khiroug
L
L
Biophysics Sector, International School for Advanced Studies (SISSA), Trieste, Italy.
Giniatullin
R
R
Talantova
M
M
Nistri
A
A
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D007700:Kinetics; D016716:PC12 Cells; D018408:Patch-Clamp Techniques; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism*
D018048:Receptors, Purinergic P2; D000255:Adenosine Triphosphate; D002118:Calcium