chapter  6
28 Pages

Chain Dancing, Super-Cool Surfactant, and Heavy Breathing: Membranes, Rafts, and Phase Transitions

ByKaushik Nag, Sangeetha Vidyashankar, Amiya K. Panda

I. Introduction 145

II. Membranes, Rafts, and Lung Surfactant 148

III. Chain Dancing 150

IV. Nanotubes Revisited 152

V. Physiological Correlates 154

VI. Supercool Surfactant 156

VII. The Cholesterol Mystery 159

VIII. Heavy Breathing: Critical Behavior Disrupted 162

IX. The Future 165

Acknowledgments 166

References 166

I. Introduction

Lung surfactant (LS) was perhaps discovered a few centuries ago by a seafarer,

Fredric Marten (1671), who described LS as, “When the whales blow up water,

they fling out with some fattish substance that floats up on the sea like sperm and

this fat the Mallemucks (sea-gulls?) devour greedily” (1). Beyond being an item

of bird feed, today we know that this material is found in all mammalian lungs

(and some other parts of the body), originates in the pulmonary type-II cells,

and its lack thereof or dysfunction causes “heavy” or distressed breathing

(2,3). We also comprehend that the LS is complex, behaves like an extracellular

membrane, although unusual in composition compared to mammalian cell mem-

branes (3,4). The physical property of the material has been studied using various

physico-chemical methodologies. The simplest of them all is Irving Langmuir’s

“phenomenon in (Alice’s!) Flatland” (5,6). These are the studies on monolayers

and some complex liquid crystalline anisotropic arrangement of molecules

in soaps (7). Surfactant is defined by DeGennes in his Nobel Lecture (1991),

“Surfactants allow us to protect a water surface and to generate beautiful soap

bubbles which delight our children” (7).