DECREASED RECEPTOR AVAILABILITY IN ABNORMALLY FLUID MEMBRANES OF NONMUSCLE CELLS IN MYOTONIC DYSTROPHY (MD)

Abstract

Decreased diphenylhexatriene fluorescence anisotropy values in MD mononuclear cells (0.163±0.017, x±SD, n= 13; controls: 0.181±0.013; p<0.01, U-test) and platelets (MD: 0.087±0.017, n=9; controls: 0.137± 0.015; p<0.001) indicate an increased plasma membrane fluidity in MD. Normal serum osmolality and simultaneously increased vasopressin plasma levels (MD: 7.4±2.1 pg/mL, n=12; controls: 4.5±1.4 pg/mL; p<0.0005) indicate reduced vasopressin sensitivity in MD. Specific binding of vasoactive intestinal peptide ([¹²⁵I]VIP; MD: 2.9± 0.9% per 10⁶ cells, n=8; controls: 5.2±1.6%; p<0.005) and VIP receptor affinity (MD: K_d=0.26±0.05 nM, n=8; controls: K_d=0.19±0.02 nM; p<0.005) were decreased in MD mononuclear cells. Our data suggest a decreased receptor availability most likely caused by a displacement of these receptors in the abnormally fluid plasma membranes of MD nonmuscle cells. This pathophysiological hypothesis explains several endocrine defects described in MD. (DFG grant Hu408/1-4)

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