Abstract
The response of mitochondrial NADHm to the increase in workload is still controversial. We measured NADHm fluorescence in isolated guinea pig ventricular myocytes stimulated at various stimulus frequency at 37°C. The NADHm fluorescence was excited at 340/20 nm, and the emission was measured at 460/50 nm. Simultaneously, the longer axis of the cell was measured by a liner image sensor with light at 540/30 nm. The membrane potential was recorded using amphotericinB perforated patch. When the positive staircase was obvious on changing the stimulus frequency from 0.1 Hz to 3.3 Hz, NADHm initially decreased by about 15.6% of control and subsequently increased to maximum levels (158% of control). When the stimulus frequency was returned to 0.1 Hz, a transient increase in NADHm was observed before returning to the control level. After treatment with ruthenium red, an inhibiter of mitochondrial calcium uniporter, this increase of NADHm during stimulating at 3.3 Hz was attenuated. We measured mitochondrial calcium (Ca2+m) using Rhod-2AM (excitation: 540/25 nm, emission: 590/55 nm) and the cell length at 710/75 nm simultaneously with the same stimulating protocol. Beat to beat Ca2+m change was recognized, and Ca2+m increased during stimulating at 3.3 Hz and returned to the control level at 0.1 Hz. The initial decrease of NADHm might be attributed to the increase of ADP ('respiratory control'). The delayed increase of NADHm suggests that Ca2+m should stimulate NADH production in response to the increased workload ('parallel activation'). [Jpn J Physiol 54 Suppl:S103 (2004)]
