Lecture notes • Taken in part from: • Adley, D. J. (1991) The Physiology of Excitable Cells, Cambridge,3ed. • Calabrese, R. C., Gordon, J., Hawkins, R., & Qian, Ning. (1995) Essentials of neural Science and Behavior. Study guide and practice problems. Appleton & Lange • Davson, H. (1970) A Textbook of General Physiology, 4th Ed., Williams and Wilkins • Hille, B. (1992) Ionic Channels of Excitable Membranes, 2ed., Sinauer. • Levitan, I. B. & Kaczmarek, L. K. (1991) The Neuron: Cell and Molecular biology, Oxford. • Mathews, G. G. (1998) Cellular Physiology of Nerve and Muscle, Blackwell Science
CELLMEMBRANE • 1) KEEPS THE CELL INTACKT (IN PART) • 2) PERMEABLE TO SMALL MOLECULES • 3) IMPERMEABLE TO LARGE MOLECULES.
DIFFUSION PHYSICAL PROCESS THAT EQUILIBRATES FREELY MOVING SUBSTANCES
CELLULAR COMPARTMENTS • INTRACELLULAR SPACE – The fluid space surrounded by the plasma membrane or cell wall. • EXTRACELLULAR SPACE – The fluid space surrounding the outside of a plasma membrane of a cell or cell wall.
OSMOLARITY • CONCENTRATION OF WATER IN SOLUTIONS CONTAINING DIFFERENT DISSOLVED SUBSTANCES.
Osmolarity (cont.) • THE HIGHER THE OSMOLARITY OF A SOLUTION THE LOWER THE CONCENTRATION OF WATER IN THAT SOLUTION.
MOLARITY • THE MOLECULAR WEIGHT, IN GRAMS, OF A SUBSTANCE DISOLVED IN 1 LITER OF SOLUTION. (1 M)
Molarity (cont.) • 1 MOLE OF DISOLVED PARTICLES PER LITER IS SAID TO HAVE 1 OSMAL
MOLALITY • MOLES OF SOLUTION PER KILOGRAM OF SOLVENT • Takes into account that large dissolved molecules (protein of high molecular weight) displace a greater volume of water than small molecules
Example • Glucose, sucrose do not greatly dissolve in water. Number of water molecules does not change.
Osmolarity • Osmolarity takes into account how many dissolved particles result from each molecule of the dissolved substance. • 0.1 M glucose solution is 0.1 Osm solution.
Glucose, sucrose and urea molecules do not dissociate when dissolved in water. • 0.1M glucose is a 0.1 Osm solution
Osmolarity for dissociated substances 0.1 M NaCl = 0.1 M Na + 0.1M Cl = 0.2 Osm
300 Osm • 300 mM glucose • 150 mM NaCl • 100 mM NaCl + 100 mM Sucrose • 75 mM NaCl + 75 mM KCl
Mixing • The mixing is caused by the random independent motion of individual molecules (temperature dependent).
Two separate actions • Random movement of the solute (glucose) • Random movement of the solvent (water).
Osmosis • WHEN SOLUTIONS OF DIFFERENT OSMOLARITY ARE PLACED IN CONTACT WITH A BARRIER THROUGH WHICH WATER WILL MOVE ACROSS THE BARRIER, WATER WILL MOVE FROM THAT SIDE WITH THE GREATER NUMBER OF WATER MOLECULES PER UNIT VOLUME (Higher Osmolarity) TO THAT SIDE WITH THE LESSER WATER MOLECULES PER UNIT VOLUME (Lower Osmolarity).
Home experiment • Mason or Kerr quart jar. • Dark Molasses • Large Carrot • Glass Tube
Observable change • Mechanism is the same, diffusion. The results of the process is observable because the water moving into the carrot displaces the molasses forcing the molasses up the tube which can be seen.
Osmotic Pressure • Suppose that one could measure the force necessary to just keep the water from moving into compartment A. • That force divided by the cross sectional area of the piston would be the osmotic pressure of the system.
Aqua pores • Pores have now been found that transfer only water and not ions.
OSMOTIC BALALANCE VS CELL VOLUME • [S]in = [S]out • [S]in + [P]in = [S]out
NO NET CHANGE WHEN IN BALANCE • IF A SUBSTANCE IS AT DIFFUSION EQUILIBRIUM ACROSS THE CELL MEMBARANE, THERE IS NO NET MOVEMENT OF THAT SUBSTANCE ACROSS THAT MEMBRANE.
Osm vs. cell volume (cont.) • REQUIRES THAT: • [S]in = [S]out • and • [S]in + [P]in = [S]out • BE SIMULATENEOUSLY TRUE AT EQUILIBRIUM.
Solution 1 • MAKE THE CELL IMPERMEANT TO WATER • Certain epithelial cells (skin) are impermanent to water
Solution 2 • PUT THE CONTENTS OF THE CELL WITHIN AN INELASTIC WALL • Plant cell’s solution
Solution 3 • MAKE THE CELL MEMBRANE IMPERMEANT TO SELECTED EXTRACELLULAR SOLUTES
[UREA]in + [P]in = [UREA]out + [SUCROSE]out
IONS IN SOLUTION (WATER) • Ions in solution behave much like particles in solution.
Na+, K+, Cl-, Ca2+ • When they move they carry their charge with them.