Superior Flexor Muscle Cells :: Biology Essays Research Papers

Effects of Extracellular Potassium Concentration on Membrane Potentials in Crayfish Superior Flexor Muscle Cells Intracellular measurement of membrane potentials in cells of the crayfish superficial flexor muscle can reveal the effects of varying the extracellular concentrations of potassium ion on the resting potential. Our results suggest that at high extracellular potassium concentrations, the resting potential resembles that of the potassium’s equilibrium potential, and at low potassium concentrations, resting potential is less related to potassium equilibrium potential. We suggest that the equilibrium potential of other ions, especially sodium, contribute more heavily to the resting potential when extracellular potassium concentration is low, which accounts for the resting potential having a less negative voltage than the potassium equilibrium potential. The determination of resting potential by the equilibrium potentials of numerous ions reduces the effect that concentration changes in any single ion will have on the resting potential, lending stability to neural cell function even during changing environmental conditions. We tested the effect of extracellular potassium concentration on membrane potentials in the crayfish superficial flexor muscle cells. We compared five different extracellular concentrations of K+ and measured resting potentials by recording extracellularly and intracellulary, using an electrode that was inserted into the muscle via a micropipette. Our results confirm the relationship between voltage across the membrane and equilibrium potentials of the most prevalent ions that is stated by the Goldman Equation. Micropipettes were constructed from capillary tubes with tip diameter of a fraction of a micron. A micropipette and holder were filled with 3M KCl; use of this saturated solution ensured that intracellular K+ did not diffuse from the cell up the pipette. The top of the holder, which connected to the Neuroprobe amplifier circuitry, contained an Ag/AgCl electrode to prevent the hydrolysis of water, which would have created bubbles of hydrogen gas that would interfere with current conduction. The crayfish superficial muscle was exposed by making a U-shaped cut in the dorsal carapace and removing the dorsal muscles, leaving only the ventral carapace, its attached muscles, and possibly the nerve cord. This region was then placed in a small plasticene dish covered with one of five crayfish Ringers’ solutions. Normal (1x) crayfish Ringer’s solution contained [K+] = 5.4 mM and was used as a control; the four experimental solutions contained [K+] of .54 (.1x), 16.2 (3x), 54 (10x), and 162 (30x) mM respectively. Despite the non-uniformity of total osmolarity, the proportion of K+ to Cl-, the other important diffusible ion, remained constant, satisfying the Donnan Equilibrium.