Has anyone ever had problems with neurons (peripheral neurons) that have little or no calcium currents? I've been seeing this in 10-50% of my rat sympathetic neurons (primary cultures) for the last ~2 years, but had never seen this issue in ~20 years before that. I've ruled out equipment (recording and tissue culture incubators) and virtually every component of my recording solutions and media. The cells look fine and I don't have problems recording other currents (Na, K, synaptic currents). I'm out of ideas.
...are you recording in whole-cell or perforated-patch conditions? L-type currents are very sensitive and may undergo rundown in intracellular perfused condition. I experienced this with Ca2+ currents and catecholamine secretion (exocytosis) in rat and mouse adrenal chromaffin cells.
Whole cell. And they're almost entirely N-type and R-type in adult rat SCGs. The weird thing is that some of the 'no current' cells (maybe 20%) will actually recover over 4-5 minutes if the cell is healthy enough to live that long. This is why I am thinking it might be an inactivation problem, but I can't think of any reason that some, but not other, cells would be depolarized.
In healthy CCs when we record in current-clamp spontaneous AP firing in perforated patches cell recordings could last more then 20 min. Perforated-patches are the only recording conditions in CCs that allow capacitance-change measurements to determine exocytosis following Ca2+ loading. You will certainly loose the fast response of the patch but the recordings of Ca2+ currents is significantly more stable and long-lasting. I suggest you to try to validate your idea that there might be an endogenous inactivation process in the background. Best,
Emilio
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