Alpha-melanocyte stimulating hormone desensitizes the responsiveness of carbon-fibres within seconds.
We monitored electrooxidation of noradrenaline and alpha-melanocyte stimulating hormone (alpha-MSH) at a carbon-fibre microelectrode (CFME). The solution of noradrenaline (1 mM) or alpha-MSH (1 mM) was applied by a pressure pulse (2 s) from a micropipette to a voltage-clamped (850 mV) CFME immersed into bathing solution of an inverted microscope chamber. The distance between the CFME and micropipette was 2 to 12 microm. The maximal currents recorded 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 the measured current. The noradrenaline-evoked anodic current was characterized by a monotonic increase that attained the maximum at the end of the pressure pulse. In contrast, the time-course of the alpha-MSH-evoked current was 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.
Arsov
Z
Z
Laboratory of Neuroendocrinology-Molecular Cell Physiology, Inst. of Pathophysiology, Medical Faculty, University of Ljubljana, Slovenia.
Zorec
R
R
D002244:Carbon; D004058:Diffusion; D004553:Electric Conductivity; D004563:Electrochemistry; D008839:Microelectrodes; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D010084:Oxidation-Reduction; D012680:Sensitivity and Specificity; D000521:alpha-MSH / Q000378:metabolism / Q000494:pharmacology*
D000521:alpha-MSH; D002244:Carbon; D009638:Norepinephrine