Electrical stimulation with Pt electrodes. V. The effect of protein on Pt dissolution

The effect of protein on the charge-induced dissolution of Pt stimulation electrodes was studied in an in vitro system. Biphasic pulses (+/- 400 mA, +/- 400 microC cm-2 geom.) were applied to smooth Pt bead electrodes (surface area = 0.03-0.08 cm2) in a buffered saline solution containing 0.075-0.2 mg/ml human serum albumin; pulse solutions were analysed periodically for dissolved Pt by flameless atomic absorption spectrometry. The incorporation of protein in the pulse solution drastically altered the dissolution behaviour of Pt electrodes. Whereas dissolution in organic saline solutions proceeded essentially in a linear fashion, the rate in protein solution decreased with time and asymptotically approached zero. The passage of electric charge was required for the observed inhibition to develop but was not required to maintain it. In contrast, the constant presence of at least 0.15 mg/ml protein in the pulse solution was required for inhibition to develop and continue. Higher concentrations of protein did not enhance the observed inhibition. These findings bear favourably on the prospect for in vivo use of Pt stimulation electrodes: the dissolution process now appears to place no greater restriction on the acceptable pulse parameters than do other irreversible reactions such as H2O electrolysis.