Z. Arsov et R. Zorec, alpha-Melanocyte stimulating hormone densensitizes the responsiveness of carbon-fibres within seconds, PFLUG ARCH, 440(5), 2000, pp. R155-R156
We monitored electrooxidation of noradrenaline and alpha-melanocyte stimula
ting hormone (alpha-MSH) at a carbon-fibre microelectrode (CFME). The solut
ion of noradrenaline (1 mM) or alpha-MSH (1 mM) was applied by a pressure p
ulse (2 s) from a micropipette to a voltage-clamped (850 mV) CFME immersed
into bathing solution of an inverted microscope chamber. The distance betwe
en the CFME and micropipette was 2 to 12 mu m. The maximal currents recorde
d for these two agents were 8.0 +/- 0.5 pA (N = 9) and 3.0 +/- 1.1 pA (N =
9), respectively. Pressure application of control solution did not affect t
he measured current. The noradrenaline-evoked anodic current was characteri
zed by a monotonic increase that attained the maximum at the end of the pre
ssure pulse. In contrast, the time-course of the alpha-MSH-evoked current w
as biphasic. The maximum amplitude of this current was attained in 0.59 +/-
0.15 s (N = 9) and then it declined with a time constant of 7.5 +/- 4.0 s
(N = 9) until the pressure pulse was terminated. We explain this phenomenon
to be due to an interaction between the peptide oxidation products and the
CFME which results in its desensitization.