Hopkins Marine Station Student Paper

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(full paper is archived in the Miller Library)

Title: Mechanism of excitation and contraction in dissociated muscle cells from the manle of Loligo opalescens
Student Author(s): Stein, Adam
Faculty Advisor(s): Gilly, William
Pages: 25
Location: Final Papers Biology 175H
Date: June 1994
Abstract: Muscle cells from the mantle of the squid Loligo opalescens were dissociated and allowed to settle on plates located with collagen. They were bathed in either high calcium medium (HCM, 10.8 mM Ca+2) or low calcium medium (LCM, 1.3 mM ca+2) and stimulated with a series of electrical shocks. The initial medium was then replaced by one with a differing calcium concentration, and the same series of shock was again administered. Cells exhibited a variety of responses to shock, but the most typical was a rapid contraction that grew stronger with increasing voltage. Switching the cells from LCM to HCM slightly increased contraction strength and slightly lowered the minimum voltage necessary to produce a twitch. Switching from high calcium to low had no discernable effect on contraction strength or threshold voltage. Likewise, the addition of tetrodotoxin until it reached a concentration of 200 nM also had no effect, regardless of the external calcium concentration. External calcium concentration in the culture medium strongly affected the cell mortality rate. Almost all cells (>90%) kept in HCM for 20 hrs were completely unresponsive to electical stimulation. By contrast, about 50% of cells kept in the LCM continued to respond to stimulation even after a period of several days.