Ca2+- and metabolism-related changes of mitochondrial potential in voltage-clamped CA1 pyramidal neurons in situ

In hippocampal slices from rats, dialysis with rhodamine-123 (Rh-123) and/o r fura-2 via the patch electrode allowed monitoring of mitochondrial potent ial (Delta Psi) changes and intracellular Ca2+ ([Ca2+](i)) of CA1 pyramidal neurons. Plasmalemmal depolarization to 0 mV caused a mean [Ca2+](i) rise of 300 nM and increased Rh-123 fluorescence signal (RFS) by less than or eq ual to 50% of control. The evoked RFS, indicating depolarization of Delta P si, and the [Ca2+](i) transient were abolished by Ca2+-free superfusate or exposure of Ni2+/Cd2+. Simultaneous measurements of RFS and [Ca2+](i) showe d that the kinetics of both the Ca2+ rise and recovery were considerably fa ster than those of the Delta Psi depolarization. The plasmalemmal Ca2+/H+ p ump blocker eosin-B potentiated the peak of the depolarization-induced RFS and delayed recovery of both the RFS and [Ca2+](i) transient. Thus the Delt a Psi depolarization due to plasmalemmal depolarization is related to mitoc hondrial Ca2+ sequestration secondary to Ca2+ influx through voltage-gated Ca2+ channels. CN- elevated [Ca2+](i) by <50 nM but increased RFS by 221% a s a result of extensive depolarization of Delta Psi. Oligomycin decreased R FS by 52% without affecting [Ca2+](i). In the presence of oligomycin, CN- a nd p-trifluoromethoxy-phenylhydrazone (FCCP) elevated [Ca2+](i) by <50 nM a nd increased RFS by 285 and 290%, respectively. Accordingly, the metabolism -related Delta Psi changes are independent of [Ca2+](i). Imaging techniques revealed that evoked [Ca2+](i) rises are distributed uniformly over the so ma and primary dendrites, whereas corresponding changes in RFS occur more l ocalized in subregions within the soma. The results show that microfluorome tric measurement of the relation between mitochondrial function and intrace llular Ca2+ is feasible in whole cell recorded mammalian neurons in situ.