HETEROGENEOUS DISTRIBUTION OF ACETYLCHOLINE-RECEPTORS IN CHICK MYOCYTES INDUCED BY CHOLESTEROL ENRICHMENT

The cholesterol concentration at the cell surface of cultured chick my ocytes was increased in order to determine the effects of high levels of cholesterol on the ion channel properties of the nicotinic acetylch oline receptor. Single channel recordings and fluorescence polarizatio n studies using 1,6-diphenyl-1,3,5-hexatriene (DPH) were performed und er equivalent conditions for normal and cholesterol enriched myocytes. In cell attached patches from myocytes with a cholesterol to phosphol ipid molar ratio (c/p) of 0.24 and a microviscosity of 1.35 poise a si ngle conductance of 51 pS was detected. The cholesterol enriched myocy tes with a c/p of 0.52 and a microviscosity of 2.05 poise showed two c onductances, a 54 pS and a 39 pS channel: both were blocked by alpha-b ungarotoxin. The 39 pS channel was detected with the simultaneous appe arance of a slow component of tau(m) (modulation time) for DPH fluores cence measured by phase demodulation. The 80% reduction in the open ti me constant (tau(2)) of the 39 pS channel suggest an inhibition of the normal conformational state. The combined results suggest that choles terol enrichment may induced a more heterogeneous lipid environment an d that the two types of channel properties could result from the distr ibution of the receptors in different domains.