Micelle Formation by Bile Salts

Abstract

Bile salts, which are soluble amphiphiles, possess a unique molecular structure when compared with typical detergent molecules. In water, bile salts form small aggregates called micelles. The behavior of bile salt micelles is quite different from micelles formed by detergents. Bile salt micelles are smaller, more highly charged and of different struc-

Effect of Intraduodenal Bile and Na-Taurodeoxycholate on Exocrine Pancreatic Secretion and on Plasma Levels of Secretin, Pancreatic Polypeptide, and Gastrin in Man

“…The amounts of TDC applied in our study are in the physiologic range and comparable with those contained in CB. The concentrations of TDC used (2G60mM) are above the critical micellar concentration and similar to those found in human gallbladder bile (20,25). Postprandial intraduodenal bile salt concentrations are lower (up to 20mM), but the TDC solutions applied have also been diluted intraduodenally by pancreatic and duodenal juice.…”

Natural Bile Acids and Synthetic Analogues Modulate Large Conductance Ca2+-activated K+ (BKCa) Channel Activity in Smooth Muscle Cells

“…Above the CMC, bile acid micelles in solution induce nonspecific membrane damage, partial membrane micellization, and/or removal of membrane proteins and lipids (Helenius et al, 1979;Coleman et al, 1980;Roda et al, 1983). Bile acids were able to effectively increase arterial smooth muscle BK Ca channel activity at concentrations well below (3 M in the application pipette) their CMCs, which would be above 1 mM under the conditions used (Carey and Small, 1972;Helenius et al, 1979;Roda et al, 1983;Heuman and Bajaj, 1994). In particular, highly polar compounds, such as cholic acid and taurolithocholic acid, which are characterized by very high CMCs and concentrations needed to achieve membrane solubilization (Helenius et al, 1979), repeatedly increased channel activity when applied in the low micromolar range to excised patches (Figs.…”

“…However, it is still possible for small bile acid aggregates to be formed at low concentrations, based on a hydrophobic interaction between the ␤-planes. In this form of aggregation, the higher the total hydrophobic index of the bile acid molecule, the higher its capability for forming aggregates (Carey and Small, 1972;Miyajima et al, 1988). The fact that two very hydrophobic derivatives, such as epilithocholic and ursocholanic acids (for which this form of aggregation would be strongly favored), were almost always ineffective activators of BK Ca channels (Fig.…”

“…This is the increased planar polarity of the bile acid molecule due to polar groups located in the bile acid hemisphere (␣ side) opposed to the hydrophobic, methyl group-containing hemisphere (␤ side) of the rings (Carey and Small, 1972;Carey, 1985;Balducci et al, 1989;Dopico et al, 2001).…”

A model for the molecular mechanism of interfacial activation of phospholipase A2 supporting the substrate theory

“…This is due to the increased distance between each pyrenephosphocholine molecule resulting in a decrement in the intermolecular pyrene excimer formation rate. Above CMC the local concentration of the pyrene phospholipid molecules was very low in the mixed miceUes, the average number of pyrenephospholipid molecules in each micelle being less than unity [28]. Upon formation of mixed micelles the rapid decrease in the Ie/Im of diPBPC would, therefore, be due to the decrement in both intra-and intermolecular excimer fluorescence ( fig.2) whereas the plateau observed in the le/lm of PBPHPC upon micelle formation should arise from the reciprocal effects of decreasing intermolecular and increasing intramolecular excimer formation.…”