Figure 6.
PKA activity is enhanced by the high superoxide levels reached during repetitive strong calcium entry. A, B, A train of three strong (100 Hz/18 sec) stimuli at 1 min intervals evoked the expected Ca2+ transients and O2- elevation (top traces). These responses were not markedly different from those induced by a single stimulus. A similar train (100 Hz/18 sec) at 5 min intervals evoked comparable Ca2+ spikes but led to further enhancement and prolongation of O2- elevations (bottom traces). C, A train of three strong (100 Hz/18 sec) stimuli at 5 min intervals (filled squares), but not single 100 Hz/18 sec or 5 Hz/180 sec pulses (filled diamonds and circles, respectively), led to a long-term increase in the fraction of dissociated catalytic Cα subunit that translocated to the nucleus, as estimated by quantitative immunocytochemistry (representative confocal images, left panels). Presumably, this reflects increased PKA activity. The increase in nuclear PKA immunofluorescence was sensitive to inhibition of mitochondrial O2- production by rotenone- oligomycin or cyanide- oligomycin (open symbols).